Company: BCDRF
Filing Date: 2025-10-23
Form Type: 6-K
Source: 0000950103-25-013553
Chunk: 0

Company: Banco Santander, S.A.
Filing Date: 2025-10-23
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 October, 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 30 July 2025 (official registry number 2844)(the “Buyback Commencement Communication”),
relating to the buyback programme of own shares (the “Buyback 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 16 and 22 October 2025 (both inclusive).

The cash amount of the
shares purchased to 22 October 2025 as a result of the execution of the Buyback Programme amounts to 833,281,564 Euros, which represents
approximately 49% of the maximum investment amount of the Buyback Programme. The programme was announced together with its other characteristics
through the Buyback Commencement Communication. With these purchases, the Bank has repurchased approximately 14.7% of its outstanding
shares as of 2021.

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