When Diana, Princess of Wales, died in Paris in 1997, her will stipulated that a share of her fortune should go to her two sons when they each turned 25. The executors, however, later decided, to change the age to 30.
For the past five years, Harry has been able to access the interest on his mother's fortune but he will be able to obtain his full entitlement only on his birthday on September 15, 'The Sunday Times' said.
He has already been entrusted with some of Diana's jewellery, which was shared between him and Prince William for the eventual use of their respective wives.
William gave his mother's sapphire engagement ring to Kate Middleton on their engagement in 2010.
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William, who turned 30 in June 2012, has already received his share of the inheritance, thought to be about 10 million pound.
A palace source told the newspaper: "The inheritance is in line with what Prince William received when he turned 30."
A palace spokesperson declined to comment on the amount Prince Harry was due to receive.