UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE TO

Tender Offer Statement under Section 14(d)(1) or 13(e)(1)

of the Securities Exchange Act of 1934

(Amendment No. 18)

Genco Shipping & Trading Limited

(Name of Subject Company (Issuer))

4 Dragon Merger Sub Inc.

(Offeror)

a direct wholly owned subsidiary of

Diana Shipping Inc.

(Parent of Offeror)

(Names of Filing Persons (identifying status as offeror, issuer or other person))

Common Stock, par value $0.01 per share

(Including the Associated Preferred Stock Purchase Rights)

(Title of Class of Securities)

Y2685T131

(CUSIP Number of Class of Securities)

Mr. Ioannis Zafirakis

Pendelis 16, Palaio Faliro

Athens, Greece J3, 175 64

30-210-947-0100

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications on Behalf of Filing Persons)

With a copy to:

Check the appropriate boxes below to designate any transactions to which the statement relates:

Check the following box if the filing is a final amendment reporting the results of the tender offer: ¨

If applicable, check the appropriate box(es) below to designate the appropriate rule provision(s) relied upon:

As permitted by General Instruction G to Schedule TO, this Schedule TO is also Amendment No. 26 (this “Amendment”) to the Schedule 13D filed by Diana Shipping Inc. (the Parent of the Offeror), on July 17, 2025 (and amended on July 31, 2025, September 30, 2025, November 24, 2025, January 13, 2026, January 16, 2026, March 10, 2026, March 23, 2026, April 13, 2026, May 4, 2026, May 7, 2026, May 12, 2026, May 18, 2026, May 19, 2026, May 27, 2026, May 28, 2026, June 1, 2026, June 2, 2026, June 4, 2026, June 8, 2026, June 11, 2026, June 12, 2026, June 15, 2026, June 16, 2026, June 17, 2026, June 18, 2026, and June 29, 2026) (collectively, as amended, the “Current Schedule 13D”) in respect of the Common Shares of the Company. Capitalized terms used but not defined in this Amendment shall have the meanings ascribed to them in the Current Schedule 13D. This Amendment amends the disclosure in the text of Items 3, 4 and 6 of the Current Schedule 13D to update information about the Reporting Person.

¹ All reported shares are owned by Diana Shipping Inc. 4 Dragon Merger Sub Inc. is a wholly-owned subsidiary of Diana Shipping Inc. Calculated based on 43,577,051 shares of common stock, par value $0.01 per share, of the Issuer outstanding as of May 6, 2026, as reported in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on May 6, 2026.

² All reported shares are owned by Diana Shipping Inc. 4 Dragon Merger Sub Inc. is a wholly-owned subsidiary of Diana Shipping Inc. Calculated based on 43,577,051 shares of common stock, par value $0.01 per share, of the Issuer outstanding as of May 6, 2026, as reported in the Issuer’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on May 6, 2026.

Item 3. Source and Amount of Funds or Other Consideration

Item 3 of the Current Schedule 13D is hereby amended and supplemented to add the following:

The information set forth in Item 4 of this Amendment is incorporated herein by reference.

Item 4 of the Current Schedule 13D is hereby amended and supplemented to add the following:

On June 30, 2026, the Reporting Person announced an extension of the fully commitment financing supporting the Reporting Person’s offer to acquire all issued and outstanding shares of Genco not already owned by the Reporting Person. The fully committed financing, in the amount of $1.412 billion, is arranged by DNB Carnegie and Nordea, with participation from leading international banks, including DNB, Nordea, BNP Paribas, Standard Chartered, Deutsche Bank and Danske Bank. An aggregate of $1.102 billion of this financing will be used, together with the Reporting Person’s available cash, to purchase the outstanding shares of Genco not already owned by the Reporting Person and for the repayment of Genco’s outstanding indebtedness.

A copy of the amendment to the commitment letter is attached as Exhibit (b)(1) hereto which is incorporated herein by reference.

Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer

Item 6 of the Current Schedule 13D is hereby amended and supplemented to add the following:

The information set forth in Item 4 of this Amendment is incorporated herein by reference.

This Amendment No. 18 to the Tender Offer Statement on Schedule TO (this “Amendment”) amends and supplements the Tender Offer Statement on Schedule TO filed with the U.S. Securities and Exchange Commission on May 4, 2026 (as it may be further amended or supplemented from time to time, the “Schedule TO”), with respect to the tender offer (the “Offer”) made by 4 Dragon Merger Sub Inc., a corporation organized under the laws of the Marshall Islands (“Purchaser”) and a direct wholly-owned subsidiary of Diana Shipping Inc., a corporation organized under the laws of the Marshall Islands (“Diana”), to purchase all of the outstanding shares of Common Stock, par value $0.01 per share (the “Common Shares”), of Genco Shipping & Trading Limited, a corporation organized under the laws of the Marshall Islands (“Genco”) (including the associated preferred stock purchase rights (the “Rights”, and together with the Common Shares, the “Shares”) issued pursuant to the Shareholder Rights Agreement, dated October 1, 2025 (as it may be further amended or supplemented from time to time), by and between Genco and Computershare Inc., as Rights Agent), other than Shares held in treasury by Genco, at $24.80 per share, net to the seller in cash, without interest and less any required withholding taxes, upon the terms and subject to the conditions set forth in the Offer to Purchase, dated May 4, 2026 (as it may be amended or supplemented from time to time, the “Offer to Purchase”) and in the related Letter of Transmittal (as it may be amended or supplemented from time to time, the “Letter of Transmittal”), copies of which are attached to the Schedule TO as Exhibits (a)(1)(A) and (a)(1)(B), respectively. On June 17, 2026, Diana submitted a revised proposal to the Board of Directors of Genco to acquire all of the issued and outstanding Common Shares not already owned by Diana for $27.34 in total implied value per share, comprised of $24.80 in cash plus one share of common stock of Diana, with the implied value based on the volume-weighted average price per Diana share for the 30 days ended on June 16, 2026 of $2.54.

Except as otherwise set forth in this Amendment, the information set forth in the Schedule TO remains unchanged. This Amendment is being filed to reflect certain updates as reflected below. Capitalized terms used but not otherwise defined herein have the meanings ascribed thereto in the Offer to Purchase or the Schedule TO, as applicable. You should read this Amendment together with the Schedule TO and the Offer to Purchase.

ITEMS 1 THROUGH 9 AND ITEM 11.

“On June 30, 2026, Diana and the Financing Sources entered into an amendment letter to the Debt Commitment Letter (the “Debt Commitment Letter Amendment”) extending the Debt Commitment Letter to September 30, 2026. The Debt Commitment Letter Amendment adjusted the commitment from the Financing Sources in respect of the voluntary refinancing of Diana’s existing debt from $331 million to $309.8 million. The refinancing of the Diana Debt is not a condition to the Offer or the availability of the Credit Facility.”

“The Financing Sources’ commitment in respect of the Credit Facility under the Debt Commitment Letter expires on September 30, 2026, unless extended.”

“On June 30, 2026, Diana and the Financing Sources entered into the Debt Commitment Letter, extending the Debt Commitment Letter to September 30, 2026. In connection therewith, Diana issued a press release announcing the extension of the Debt Commitment Letter, a copy of which is attached hereto.”

ITEM 12. EXHIBITS.

Item 12 of the Schedule TO is hereby amended and supplemented by adding the following Exhibits:

SIGNATURE

After due inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: June 30, 2026

ATTACHMENTS / EXHIBITS

EXHIBIT (A)(5)(X)

EXHIBIT (B)(2)