HOLLYWOOD: Keira Knightley has posed nude for a portrait. The ‘Atonement’ star has reportedly been visiting London’s Halcyon Gallery to be painted naked by artist Mitch Griffiths for a new exhibition. A source said: “It’s considered a great honour to be painted by Mitch. He is a highly respected nude painter and is painting as number of subjects for a new exhibition next year. He is delighted Keira decided to take part.” The 24-year-old actress – who is widely considered to be one of Hollywood’s most beautiful women – is currently starring in play ‘The Misanthrope’, which is running in London’s West End theatre district. In the production, a modern-day version of Moliere's 17th Century comedy work, Keira plays a vacuous Hollywood starlet.