Pop star Lily Allen stepped back into the spotlight on Thursday (31Oct13) by dressing as an alien and performing with fellow Brit Robbie Williams to raise cash for Syrian refugees at a Halloween charity event. The Smile hitmaker, who has been on hiatus since 2010, donned green body paint, a green sequinned dress, and green leopard print tights to attend the United Nations Children's Fund (UNICEF) moneyraiser. She and former Take That star Williams performed a duet together before mingling with other star guests, including model Jodie Kidd and socialite Jemima Khan, at the event in London. Actor Ewan McGregor, a UNICEF ambassador, also joined Williams for a surprise rendition of his hit track Angels. Meanwhile, other stars were enjoying a scary night out at the annual Halloween house party thrown by TV presenter Jonathan Ross. Nicole Scherzinger dressed as Catwoman for the bash, Simon Pegg revisited his hit movie Shaun of the Dead to pose as a blood-soaked zombie, and Kate Moss and her rocker husband Jamie Hince arrived as Mexican 'Day of the Dead' dolls. Ross holds a star-studded Halloween party every year at his north London home.