Amy Winehouse was the other new entry in the Britain's Richest Young Millionaires list while soon-to-be-wed Wayne Rooney and Coleen McLoughlin tied with Princes William and Harry.
The list, which is part of the Sunday Times Rich List, recorded Leona Lewis, 23, as being worth £6 million after finding fame on both sides of the Atlantic.
Leona: Worth £6million just 18 months after winning X Factor
She is the first British solo artist to have a debut album top the US charts, and in Britain she had the biggest selling single of 2007 with Bleeding Love.
Her global career is being masterminded by X Factor judge, Simon Cowell.
Troubled Winehouse, 24, has sold five million copies of her most recent album, Back to Black, and her popularity in the United States has earned her five Grammy Awards, while she has also been nominated for three Ivor Novello songwriting awards.
Wayne and Coleen tie with Princes William and Harry in the young rich list
Rooney and Coleen have a joint wealth of £35 million which ties them in 13th place in the young millionaires list with Wills and Harry.
Also making an appearance in the young rich list were 18-year-old Harry Potter stars Daniel Radcliffe who is worth £20 million, and Emma Watson, 18, who has £10 million.
Actress Keira Knightley, 23, has £18 million while footballer Michael Owen, is the richest young footballer with an estimated £41 million.
