Exhibit 10.21

SECOND AMENDED AND RESTATED PROMISSORY NOTE

$75,000,000.00 November 3, 2021

FOR VALUE RECEIVED, each of KBSIII 60 SOUTH SIXTH STREET, LLC, a Delaware limited liability company (“RBC Plaza Borrower”), KBSIII PRESTON COMMONS, LLC, a Delaware limited liability company (“Preston Commons Borrower”), KBSIII STERLING PLAZA, LLC, a Delaware limited liability company (“Sterling Plaza Borrower”), KBSIII TOWERS AT EMERYVILLE, LLC, a Delaware limited liability company (“Towers at Emeryville Borrower”), KBSIII TEN ALMADEN, LLC, a Delaware limited liability company (“Ten Almaden Borrower”), and KBSIII LEGACY TOWN CENTER, LLC, a Delaware limited liability company (“Legacy Town Center Borrower”; RBC Plaza Borrower, Preston Common Borrower, Sterling Plaza Borrower, Towers at Emeryville Borrower, Ten Almaden Borrower, and Legacy Town Center Borrower shall be hereinafter referred to, individually, as a “Borrower” and, collectively, jointly and severally, as “Borrowers”) hereby promises to pay to the order of U.S. BANK, NATIONAL ASSOCIATION, a national banking association (“Lender”), as one of the lenders under that certain Amended and Restated Loan Agreement (defined below) by and among Borrowers, the lenders from time to time a party thereto (collectively, the “Lenders”), and Bank of America, N.A., a national banking association (together with any and all of its successors and assigns, “Administrative Agent”) as administrative agent for the benefit of the lenders (the “Loan Agreement”) of even date herewith, without offset, in immediately available funds in lawful money of the United States of America, at the Administrative Agent’s Office as defined in the Loan Agreement, the principal sum of SEVENTY-FIVE MILLION AND NO/100 DOLLARS ($75,000,000.00) (or the unpaid balance of all principal advanced against this Note, if that amount is less), together with interest on the unpaid principal balance of this Note from day to day outstanding as hereinafter provided. Capitalized terms used herein and not otherwise defined herein shall have the meanings ascribed to such terms in the Loan Agreement. This Note amends and restates in its entirety that certain Amended and Restated Promissory Note, dated November 17, 2017, executed by Borrowers and payable to the order of Lender (the “Original Note”). In no event shall this Note be deemed to be or constitute a novation or release of Borrowers’ obligations under the Original Note.

1.Note; Interest; Payment Schedule. This Note (as may be amended, modified, supplemented, restated and replaced from time to time, this “Note”) is one of the Notes referred to in the Loan Agreement and is entitled to the benefits thereof and subject to prepayment in whole or in part as provided therein. The entire principal balance of this Note then unpaid shall be due and payable at the times as set forth in the Loan Agreement. Accrued unpaid interest shall be due and payable at the times and at the interest rate as set forth in the Loan Agreement until all principal and accrued interest owing on this Note shall have been fully paid and satisfied. Any amount not paid when due and payable hereunder shall, to the extent permitted by applicable Law, bear interest and if applicable a late charge as set forth in the Loan Agreement.

2.Security; Loan Documents. The security for this Note includes the Security Instruments (as defined in the Loan Agreement). This Note, the Security Instruments, the Loan Agreement and all other documents now or hereafter securing, guaranteeing or executed in connection with the loan evidenced, in whole or in part, by this Note (the “Loan”), are, as the same

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have been or may be amended, restated, modified or supplemented from time to time, herein sometimes called individually a “Loan Document” and together the “Loan Documents.”

3.Defaults.

(a)Upon the occurrence and during the continuance of a Default, Administrative Agent on behalf of the Lender and the other Lenders shall have the right to declare the unpaid principal balance and accrued but unpaid interest on this Note, and all other amounts due hereunder and under the other Loan Documents, at once due and payable (and upon such declaration, the same shall be at once due and payable), to foreclose any liens and security interests securing payment hereof and to exercise any of its other rights, powers and remedies under this Note, under any other Loan Document, or at Law or in equity.

(b)All of the rights, remedies, powers and privileges (together, “Rights”) of Administrative Agent on behalf of the Lender and the other Lenders provided for in this Note and in any other Loan Document are cumulative of each other and of any and all other Rights at Law or in equity. The resort to any Right shall not prevent the concurrent or subsequent employment of any other appropriate Right. No single or partial exercise of any Right shall exhaust it or preclude any other or further exercise thereof, and every Right may be exercised at any time and from time to time. No failure by Administrative Agent, Lender and the other Lenders to exercise, and no delay in exercising any Right, including, but not limited to, the right to accelerate the maturity of this Note, shall be construed as a waiver of any Default or as a waiver of any Right. Without limiting the generality of the foregoing provisions, the acceptance by the holder hereof from time to time of any payment under this Note which is past due or which is less than the payment in full of all amounts due and payable at the time of such payment, shall not (i) constitute a waiver of or impair or extinguish the right of Administrative Agent, Lender and the other Lenders to accelerate the maturity of this Note or to exercise any other Right at the time or at any subsequent time, or nullify any prior exercise of any such Right, (ii) constitute a waiver of the requirement of punctual payment and performance or a novation in any respect, or (iii) in any way excuse the existence of a Default.

(c)If any Borrower sues any holder in connection with this Note or any other Loan Document and does not prevail, then Borrowers agree to pay to each such holder to the extent required under Section 4.15 of the Loan Agreement, in addition to principal, interest and any other sums owing to Administrative Agent, Lender and the other Lenders hereunder and under the other Loan Documents, all costs and expenses incurred by such holder in any such suit or proceeding, including attorneys’ fees and expenses, investigation costs and all court costs.

4.Heirs, Successors and Assigns. The terms of this Note and of the other Loan Documents shall bind and inure to the benefit of each Borrower and Lender and their respective successors and assigns permitted by the Loan Agreement. The foregoing sentence shall not be construed to permit any Borrower to assign the Loan except as otherwise permitted under the Loan Agreement. As further provided in the Loan Agreement, Lender may, at any time, sell, transfer, or assign all or a portion of its interest in this Note, the Security Instruments and the other Loan Documents, as set forth in the Loan Agreement.

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5.General Provisions. Time is of the essence with respect to Borrowers’ obligations under this Note. If more than one Person executes this Note as “Borrower” or “Borrowers,” all of said parties shall be jointly and severally liable for payment of the indebtedness evidenced hereby. Each Borrower and all sureties, endorsers, guarantors and any other party now or hereafter liable for the payment of this Note in whole or in part, hereby severally (a) waive demand, presentment for payment, notice of dishonor and of nonpayment, protest, notice of protest, notice of intent to accelerate, notice of acceleration and all other notices (except any notices which are specifically required by this Note or any other Loan Document), filing of suit and diligence in collecting this Note or enforcing any of the security herefor; (b) agree to any substitution, subordination, exchange or release of any such security or the release of any party primarily or secondarily liable hereon; (c) agree that neither Administrative Agent, Lender nor any other Lender shall be required first to institute suit or exhaust its remedies hereon against any Borrower or others liable or to become liable hereon or to perfect or enforce its rights against them or any security herefor; (d) consent to any extensions or postponements of time of payment of this Note for any period or periods of time and to any partial payments, before or after maturity, and to any other indulgences with respect hereto, without notice thereof to any of them; (e) waive the benefit of all homestead and similar exemptions as to this Note; (f) agree that their liability under this Note shall not be affected or impaired by any determination that any security interest or lien taken by Administrative Agent, Lender or any other Lender to secure this Note is invalid or unperfected; and (g) hereby subordinate any and all rights against any other Borrower and any of the security for the payment of this Note, whether by subrogation, agreement or otherwise, until this Note is paid in full. A determination that any provision of this Note is unenforceable or invalid shall not affect the enforceability or validity of any other provision and the determination that the application of any provision of this Note to any Person or circumstance is illegal or unenforceable shall not affect the enforceability or validity of such provision as it may apply to other Persons or circumstances. This Note may not be amended except in a writing specifically intended for such purpose and executed by the party against whom enforcement of the amendment is sought. Captions and headings in this Note are for convenience only and shall be disregarded in construing it. The words “include” and “including” shall be interpreted as if followed by the words “without limitation.” THIS NOTE, AND ITS VALIDITY, ENFORCEMENT AND INTERPRETATION, SHALL BE GOVERNED BY CALIFORNIA LAW (WITHOUT REGARD TO ANY CONFLICT OF LAWS PRINCIPLES) AND APPLICABLE UNITED STATES FEDERAL LAW.

6.Notices. Any notice, request, or demand to or upon any Borrower or the holder hereof shall be deemed to have been properly given or made when delivered in accordance with the Loan Agreement.

7.No Usury. It is expressly stipulated and agreed to be the intent of Borrowers, Administrative Agent and all Lenders at all times to comply with applicable state Law or applicable United States federal Law (to the extent that it permits a Lender to contract for, charge, take, reserve, or receive a greater amount of interest than under state Law) and that this Section shall control every other covenant and agreement in this Note and the other Loan Documents. If applicable state or federal Law should at any time be judicially interpreted so as to render usurious any amount called for under this Note or under any of the other Loan Documents, or contracted for, charged, taken, reserved, or received with respect to the Loan, or if Administrative Agent’s exercise of the option to accelerate the Maturity Date, or if any prepayment by Borrowers results in Borrowers’ having paid any interest in excess of that permitted by applicable Law, then it is

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Administrative Agent’s and each Lender’s express intent that all excess amounts theretofore collected by Administrative Agent or any Lender shall be credited on the principal balance of this Note and all other indebtedness and the provisions of this Note and the other Loan Documents shall immediately be deemed reformed and the amounts thereafter collectible hereunder and thereunder reduced, without the necessity of the execution of any new documents, so as to comply with the applicable Law, but so as to permit the recovery of the fullest amount otherwise called for hereunder or thereunder. All sums paid or agreed to be paid to Lenders for the use, forbearance, or detention of the Loan shall, to the extent permitted by applicable Law, be amortized, prorated, allocated, and spread throughout the full stated term of the Loan until payment in full so that the rate or amount of interest on account of the Loan does not exceed the maximum lawful rate from time to time in effect and applicable to the Loan for so long as the Loan is outstanding.

THE LOAN DOCUMENTS REPRESENT THE FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES.

THERE ARE NO ORAL AGREEMENTS BETWEEN THE PARTIES.

[Signatures begin on following page.]

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IN WITNESS WHEREOF, each Borrower has duly executed and delivered this Second Amended and Restated Note as of the date first above written.

KBSIII 60 SOUTH SIXTH STREET, LLC, a Delaware limited liability company
By:	KBSIII REIT ACQUISITION VII, LLC, a Delaware limited liability company, its sole member
	By:	KBS REIT PROPERTIES III, LLC, a Delaware limited liability company, its sole member
		By:	KBS LIMITED PARTNERSHIP III, a Delaware limited partnership, its sole member
			By:	KBS REAL ESTATE INVESTMENT TRUST III, INC., a Maryland corporation, its general partner
				By:	/s/ Charles J. Schreiber, Jr. Charles J. Schreiber, Jr., Chief Executive Officer

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KBSIII PRESTON COMMONS, LLC, a Delaware limited liability company
By:	KBSIII REIT ACQUISITION IX, LLC, a Delaware limited liability company, its sole member
	By:	KBS REIT PROPERTIES III, LLC, a Delaware limited liability company, its sole member
		By:	KBS LIMITED PARTNERSHIP III, a Delaware limited partnership, its sole member
			By:	KBS REAL ESTATE INVESTMENT TRUST III, INC., a Maryland corporation, its general partner
				By:	/s/ Charles J. Schreiber, Jr. Charles J. Schreiber, Jr., Chief Executive Officer

[Signatures continue on following page.]

KBSIII STERLING PLAZA, LLC, a Delaware limited liability company
By:	KBSIII REIT ACQUISITION VIII, LLC, a Delaware limited liability company, its sole member
	By:	KBS REIT PROPERTIES III, LLC, a Delaware limited liability company, its sole member
		By:	KBS LIMITED PARTNERSHIP III, a Delaware limited partnership, its sole member
			By:	KBS REAL ESTATE INVESTMENT TRUST III, INC., a Maryland corporation, its general partner
				By:	/s/ Charles J. Schreiber, Jr. Charles J. Schreiber, Jr., Chief Executive Officer

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KBSIII TOWERS AT EMERYVILLE, LLC, a Delaware limited liability company
By:	KBSIII REIT ACQUISITION XXI, LLC, a Delaware limited liability company, its sole member
	By:	KBS REIT PROPERTIES III, LLC, a Delaware limited liability company, its sole member
		By:	KBS LIMITED PARTNERSHIP III, a Delaware limited partnership, its sole member
			By:	KBS REAL ESTATE INVESTMENT TRUST III, INC., a Maryland corporation, its general partner
				By:	/s/ Charles J. Schreiber, Jr. Charles J. Schreiber, Jr., Chief Executive Officer

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KBSIII TEN ALMADEN, LLC, a Delaware limited liability company
By:	KBSIII REIT ACQUISITION XIX, LLC, a Delaware limited liability company, its sole member
	By:	KBS REIT PROPERTIES III, LLC, a Delaware limited liability company, its sole member
		By:	KBS LIMITED PARTNERSHIP III, a Delaware limited partnership, its sole member
			By:	KBS REAL ESTATE INVESTMENT TRUST III, INC., a Maryland corporation, its general partner
				By:	/s/ Charles J. Schreiber, Jr. Charles J. Schreiber, Jr., Chief Executive Officer

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KBSIII LEGACY TOWN CENTER, LLC, a Delaware limited liability company
By:	KBSIII REIT ACQUISITION III, LLC, a Delaware limited liability company, its sole member
	By:	KBS REIT PROPERTIES III, LLC, a Delaware limited liability company, its sole member
		By:	KBS LIMITED PARTNERSHIP III, a Delaware limited partnership, its sole member
			By:	KBS REAL ESTATE INVESTMENT TRUST III, INC., a Maryland corporation, its general partner
				By:	/s/ Charles J. Schreiber, Jr. Charles J. Schreiber, Jr., Chief Executive Officer