Celebrity Stars In Masks! Who's that pig? See Keira Knightley and other stars (Britney! Celine!) wearing wacky masks By People Staff Published on April 9, 2008 04:00 PM Share Tweet Pin Email Trending Videos 01 of 10 KEIRA KNIGHTLEY Ramey; Matrix/Bauer-Griffin The actress and her friends hammed it up for Knightley's 21st birthday party at London's Café Royal. 02 of 10 BRITNEY SPEARS Fame; INF (inset) The pop star cha cha cha-ed out of Hollywood club The Green Door in a sombrero and eye-mask with amiga Alli Sims (not pictured). 03 of 10 DIDDY Roger Wong/INF The 'P' was for party, not V for Vendetta, when the Bad Boy Records mogul hit a Halloween Party at New York's Cipriani restaurant. 04 of 10 GWYNETH PALTROW Bauer-Griffin;Nick Price/Startraks(inset) Paltrow hopped around New York with daughter Apple in search of Halloween candy. 05 of 10 PRINCE HARRY Goff/INF; Tim Ockenden/AP The Commodore-in-Chief of small ships and diving gets wet on a visit to the Royal Navy's diving squadron in Portsmouth, England. 06 of 10 ASHLEY OLSEN Flynet Olsen donned a mask to hide her face from photographers at Hollywood stylist Estee Stanley's wedding. 07 of 10 PETE WENTZ Scott Kirkland/INF; Jen Lowery/Startraks (inset) The Fall Out Boy bassist hit the red carpet at the MTV Video Music Awards in a green-as-a-gecko mask. 08 of 10 MICHAEL JACKSON Wenn; MJ Kim/Getty (inset) The Gloved One became the Hooded One during a shopping spree on Melrose in L.A. 09 of 10 CELINE DION Newspix/Rex USA; Landov (inset) Feeling under the weather while Down Under, the songstress wasn't taking any during her 2008 Taking Chances world tour. 10 of 10 JAMES GANDOLFINI Hector Vallenilla/Pacific Coast News And you thought Tony Soprano was a killer. Gandolfini – dressed up as Jason from Friday the 13th – goes trick-or-treating in New York.