Company: BCDRF
Filing Date: 2025-08-01
Form Type: 6-K
Source: 0000950103-25-009669
Chunk: 0

Company: Banco Santander, S.A.
Filing Date: 2025-08-01
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 August, 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. (“Banco Santander”),
in compliance with the Securities Market legislation, hereby reports the following:

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

Banco Santander reports the results it has obtained
in the most recent stress test exercise carried out by the European Banking Authority (EBA) and the European Central Bank (ECB).

The exercise covered a three-year period (end of
2024 – end of 2027) with two scenarios (baseline and adverse) applied to the consolidated perimeter of Grupo Santander. The CET1
ratio is a financial solvency ratio whose implementation by the institutions is being carried out progressively, in accordance with the
transitional implementation schedules of the modifications of Directive 2013/36/EU of the European Parliament and of the Council of 26 June
2013 (the “Capital Requirements Directive”) and Regulation (EU) No 575/2013 of the European Parliament
and of the Council of 26 June 2013 (the “Capital Requirements Regulation”)
and International Financial Reporting Standard (“IFRS”) 9.

During the phase-in period of these regulations,
in addition to the CET1 Phased-in ratio (a capital ratio calculated pursuant to the transitional regime), which is the legally applicable
ratio, the Fully-loaded CET1 ratio (a capital ratio calculated assuming a full implementation of the aforementioned regulations) is also
used for information purposes.

The stress test exercise results in the following
projected capital ratios for Grupo Santander for the periods