Alexander Abramov, Evraz’s longstanding chairman who owns nearly 20pc of the company, also resigned. Aleksey Ivanov, its chief executive, is now the only remaining director.

During his time with the prince, Sir Michael helped organise the heir to the throne’s wedding to the Duchess of Cornwall in 2005.

He also led the 2003 investigation into allegations of misconduct within Charles’s household, including claims that unwanted royal gifts were being sold off, but the inquiry found no evidence of serious wrongdoing.

Prince Charles’s charitable body is facing a separate, unconnected police investigation into an alleged “cash-for-honours” scandal.

Sir Michael’s father was a Privy Purse auditor, as was his great-grandfather William Barclay Peat, and a founding partner of accountancy firm Peat Marwick, which later became the global accountancy firm KPMG.

A product of Eton and Trinity College, Oxford, Sir Michael became a partner at KPMG before joining the Royal Household.

Evraz said it was “deeply concerned and saddened by the Ukraine-Russia conflict and hopes that a peaceful resolution will be found soon”.