must I inform them if there is a new shareholder

Yes, usually in case of a change in the UBO structure

A new shareholder often changes who the ultimate beneficial owner is, and that is exactly what a bank must keep track of on the basis of the customer due diligence required by the Anti-Money Laundering and Countering the Financing of Terrorism Act. As soon as the shareholding is large enough to designate someone as a UBO — typically from an interest of more than 25% — the bank expects an update to your file. In the case of a small minority holding without decisive control, this is less often the case, but the bank determines this itself on the basis of its own risk assessment, not you.

In practice, you will receive this as a separate question in the bank's periodic KYC update, separate from the questionnaires on sustainability or cybersecurity that you complete otherwise. If you have already had the new shareholder structure processed in the Business Register, that is usually the supporting document the bank wants to see: a recent extract or the underlying shareholder register. If that update is still missing, you can usually do nothing more in the meantime than indicate that the change is being processed. How you describe the UBO structure yourself in a questionnaire is explained on the page about who are the ultimate beneficial owners of the company.

Where that follows from: AMLCFT Act and Business Register Act

The obligation to inform the bank who the UBOs are follows from the ongoing customer due diligence that banks must conduct under the Anti-Money Laundering and Countering the Financing of Terrorism Act — that act obliges the bank, not the entrepreneur, to keep that information current, but in practice this can only happen if the customer reports the change. Apart from that, the shareholder change must be processed in the business register anyway under the Business Register Act 2007, and that extract is immediately the document with which you provide the bank. If you are unsure whether a specific question in a portal concerns the UBO or something else such as sanctions screening, the explanation on the page about what exactly a bank means by UBO data in a questionnaire.