Company: BCDRF
Filing Date: 2025-05-14
Form Type: 6-K
Source: 0000950103-25-005980
Chunk: 0

Company: Banco Santander, S.A.
Filing Date: 2025-05-14
Form: 6-K
Chunk 0
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<div align='center'>FORM 6-K

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Report of Foreign Issuer

Pursuant to Rule 13a-16 or 15d-16 of

the Securities Exchange Act of 1934

For the month of May, 2025

Commission File Number: 001-12518

Banco Santander, S.A.

(Exact name of registrant as specified in its charter)

Ciudad Grupo Santander

28660 Boadilla del Monte (Madrid) Spain

(Address of principal executive office)</div>

Indicate by check mark whether the registrant files or will file annual
reports under cover of Form 20-F or Form 40-F:

| Form 20-F | X |     | Form 40-F |

<div align='center'>Banco Santander, S.A.

TABLE OF CONTENTS</div>

Item 1

Banco Santander, S.A.(the “Bank”
or “Banco Santander”), in compliance with the Securities Market legislation, hereby communicates the following:

<div align='center'>OTHER RELEVANT INFORMATION</div>

Reference is made to our notice of inside information of 5 February 2025 (official registry number 2584)(the “Buy-back Commencement Communication”),
relating to the buyback programme of own shares (the “Buy-back Programme”) approved by the Board of Directors of Banco
Santander.

Pursuant to article 5 of Regulation (EU) no. 596/2014
on Market Abuse of 16 April 2014, and articles 2.2 and 2.3 of Commission Delegated Regulation (EU) 2016/1052, of 8 March 2016, the Bank
informs of the transactions carried out over its own shares between 7 and 13 May 2025 (both inclusive).

The cash amount of the shares purchased to 13 May 2025as a result of the execution of the Buy-back Programme amounts to 1,454,331,171 Euros, which represents approximately
91.6% of the maximum investment amount of the Buy-back Programme. The programme was announced together with its other characteristics
through the Buy-back Commencement Communication. With these purchases, the Bank has repurchased approximately 14% of its outstanding shares
as of 2021.

| Date       | Security | Transaction | Trading venue | Number of shares