King Charles III has paid more than £30 million ($39.6 million) in personal taxes since becoming monarch in September 2022, Buckingham Palace announced Thursday, in the first such disclosure by a reigning British sovereign.

The palace, which had confirmed at the weekend that it would make the unprecedented release, said it was part of its "commitment to transparency" as royal finances come under increasing public scrutiny.

Charles's eldest son and heir Prince William also for the first time revealed his personal tax information, having paid more than £20 million in taxes since inheriting the title of Prince of Wales when his father became king.

UK monarchs are legally exempt from paying certain taxes, though they have paid some duties voluntarily for decades, and they also have no obligation to disclose their private tax bills.

"The amount of tax payable by His Majesty since Accession is more than £30 million," the palace said within a wider press release updating various aspects of royal finances.

It noted in the two full tax years since he acceded to the throne on September 10, 2022, his personal bill was £24.6 million. 

That comprised £11.7 million in 2023-24 and £12.9 million in 2024-25. Tax years in Britain run from early April. 

It did not give the figure for 2022 to 2023.

William, 44, paid more than £20 million in income and capital gains taxes since inheriting the title when Charles became king.

He stumped up £8.34 million in 2023-24 and £7.76 million in the 2024-25 tax year.