That single ticket was worth $233.1 million, The Daily Telegraph reported Saturday.
The ticket holder has come forward, but the ticket must still be validated, said a spokesman for the National Lottery.
It's the seventh time since January that a Briton has won the transnational lottery.
If the ticket is validated, the winner will be wealthier than Prince William and Prince Harry, whose land inheritance is valued at $44 million, according to the Sunday Times Rich List 2012. Actor Daniel Radcliffe of Harry Potter fame is worth $84.7 million, while pop singer Adele is worth $31.3 million.
Other big Euromillions winnings by Britons include prizes of $177.3 million in October 2010 and $158.4 million a year later.
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