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 June, 2026

 

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)

 

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
 
 

 

 

 

 

 

Banco Santander,
S.A.

 

TABLE OF CONTENTS

 

Item 

 

 
 

1
Report of Other Relevant Information dated June 11, 2026

 

Item
1 

 

 

 

 

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

 

OTHER RELEVANT INFORMATION

 

Reference is made
to our notice of inside information of 4 February 2026 (official registry number 3077) (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 4 and 10 June (both inclusive).

 

The cash amount of the shares purchased to 10 June
2026 as a result of the execution of the Buyback Programme amounts to 3,256,642,080 Euros, which represents approximately 64.7% 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 17.1% of its outstanding shares as of 2021.

 

Date
Security
Transaction
Trading venue
Number of shares

Weighted average

price (€)

04/06/2026
SAN
Purchase
XMAD
2,802,684
10.6847

04/06/2026
SAN
Purchase
CEUX
1,500,000
10.6860

05/06/2026
SAN
Purchase
XMAD
2,352,232
10.7605

05/06/2026
SAN
Purchase
CEUX
1,200,000
10.7601

05/06/2026
SAN
Purchase
AQEU
192,929
10.7502

08/06/2026
SAN
Purchase
XMAD
4,140,498
10.6561

08/06/2026
SAN
Purchase
CEUX
1,981,645
10.6569

08/06/2026
SAN
Purchase
TQEX
148,484
10.6526

08/06/2026
SAN
Purchase
AQEU
301,932
10.6612

09/06/2026
SAN
Purchase
XMAD
2,755,418
10.7073

09/06/2026
SAN
Purchase
CEUX
1,226,247
10.6914

10/06/2026
SAN
Purchase
XMAD
5,482,844
10.4961

10/06/2026
SAN
Purchase
CEUX
2,383,000
10.4951

10/06/2026
SAN
Purchase
TQEX
245,000
10.4945

10/06/2026
SAN
Purchase
AQEU
663,000
10.4953

 
 
 
TOTAL
27,375,913
 

 

Issuer name: Banco Santander, S.A. – LEI
5493006QMFDDMYWIAM13

 

Reference of the financial instrument: ordinary
shares – Code ISIN ES0113900J37

 

Detailed information of the transactions carried
out within the referred period is attached as Annex I.

 

Boadilla del Monte (Madrid), 11 June 2026

 

 

 

 

ANNEX I

 

Detailed information on each of the transactions
carried out within the context of the Buy-back Programme between 04/06/2026 and 10/06/2026 (both inclusive)

 

(https://www.santander.com/content/dam/santander-com/es/documentos/cumplimiento/do-anexo-i-04-a-10-junio-2026-es.pdf)

 

SIGNATURE

 

Pursuant to the
requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned,
thereunto duly authorized.

 

 
Banco Santander, S.A.

 
 

 
 

Date:
June 11, 2026
By:
     /s/ Pedro de Mingo Kaminouchi

 
 
 
Name:
Pedro de Mingo Kaminouchi

 
 
 
Title:
Head of Corporate Compliance