Emma Watson has been given 10.5 million pounds (NZ$26m) for her birthday.
Watson, who plays Harry Potter's sidekick Hermione Granger in the wizard film series, was handed the fortune upon turning 18 yesterday.
The actress has promised to attend 'millionaire school' in order to learn how to responsibly handle her accounts, which will be managed by the English bank Coutts, who look after Queen Elizabeth's account.
A source said: "It was Emma parents Chris and Jacqueline who opened her Coutts account. The idea is for the money to grow and safeguard her future - not be blown in a couple of years.
Emma is now surrounded by several trusted private bankers who will advise her on her spending."
Watson is rumoured to be earning 2.5 million pounds ($6.2m) for her role in the sixth film Harry Potter and the Half-Blood Prince, upped by studio bosses after she threatened to pull out of the lucrative franchise to attend university.
Watson's coming of age also presents a worry for Harry Potter producers who are keen to keep the main stars out the limelight.
She recently sparked concern after being seen at several parties in London and striking up an unlikely friendship with Razorlight rocker Johnny Borrell.
Watson has been signed to model agency Storm, who previously discovered Kate Moss.
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