Company: BCDRF
Filing Date: 2025-10-31
Form Type: 424B5
Source: 0001193125-25-260533
Chunk: 27

Company: Banco Santander, S.A.
Filing Date: 2025-10-31
Form: 424B5
Chunk 27
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2025 (Accession                                                                                                                                               
 No. 0000891478-25-000113), which are incorporated by reference in this prospectus supplement, for risks involved with an investment in the Notes.                                                                                       |

S-14

RISK FACTORS

Before purchasing the Notes, you should consider carefully the information under the heading “Risk Factors” in the Group’s Annual Report on Form 20-Ffor the year ended December31, 2024 and under the heading “Part 2. Supplemental Information—Item 4. Risk Factors” in the Group’s Report on Form 6-Kfiled with the SEC on July31, 2025 (Accession No.0000891478-25-000113),which are incorporated by reference herein. The Notes are also subject to the risks identified in the accompanying prospectus under the headings “Risks Relating to the Securities,” “Risks Relating to the Debt Securities” and “Risks Related to the Senior Non Preferred Debt Securities.” You should also carefully consider the other information included in this prospectus supplement, the accompanying prospectus and other information incorporated by reference herein and therein. Each of the risks described in these documents could materially and adversely affect our business, financial condition, results of operations and prospects, or could result in a partial or complete loss of your investment. See “Where You Can Find More Information” in the accompanying prospectus.

Risks Relating to the Notes

The following discussion supplements the information under the heading “Risk Factors” in the accompanying prospectus.

There are limitations to our gross-upobligation on the Notes.

Our obligation to pay Additional Amounts in respect of any withholding or deduction in respect of taxes on the Notes of any series applies only
to payments of interest and not to payments of principal or premium, as described under “Description of the Notes—Additional Amounts.” Therefore, we will not be required to pay any Additional Amounts on the Notes of any
series with respect to any withholding or deduction applied to payments of principal or amounts payable on redemption. Accordingly, if any such withholding or deduction were to apply to any payments of principal or redemption amounts on the Notes of
any series, holders of Notes of such series may receive less than the full amount due under the Notes of such series, and the market value of the Notes of any series may be adversely affected.

Risks Relating to the 2030 Floating Rate Notes

The following discussion supplements the information under the heading “Risk Factors” in the accompanying