06/21/2007 AT 03:30 PM EDT
turned 25 on Thursday – and his bank account got a serious boost.
The prince now has access to the interest – an estimated $500,000 to $600,000 a year – generated by the $13 million left to him by his mother, Princess Diana, who died in 1997.
He'll come into the full capital sum when he turns 30. His brother Harry, 22, will gain access to his inheritance – a similar amount – on the same schedule, according to their mother's will.
Reps for the prince would not say what he plans to do with the money, the Associated Press reports.
He and Harry each earn about $44,000 a year as second lieutenants in the British army, and their necessities – including housing, staff and polo playing – are paid for by their father, Prince Charles.
According to Britain's Guardian
newspaper, William was expected to spend his birthday training with the army in Dorset.