On 12 April 2007, it was announced that Halliwell had signed a six-book deal with Macmillan Children's Books. The books follow the adventures of nine-year-old Ugenia, a character based on Halliwell, alongside her friends Bronte, Rudy, and Trevor. The character Princess Posh Vattoria, a caricature of Halliwell's bandmate Victoria Beckham, was featured in early drafts, but has not appeared in the book series. Other characters are said by Halliwell to be loosely based on Gordon Ramsay, George Michael, Marilyn Monroe, Vincent van Gogh, Wayne Rooney and the character Justin Suarez from the TV series "Ugly Betty". According to the official site, the book sold more than 250,000 copies in its first 5 months, making Halliwell 2008's most successful female celebrity children's author.