Mischa Barton wore a hot-pink swimsuit to hit the beach with her boyfriend, Sebastian Knapp, in Ibiza today. The couple ventured into the water, then retreated to the sand for kisses. The day in the sun came after Mischa and Sebastian joined British celebs like Pixie Geldof and Nick Grimshaw for the launch of DJ Tiesto's collection for Guess at Ibiza's Lio restaurant on Tuesday. Mischa and Sebastian are off in Spain, away from their current home base in London. Sebastian, a UK actor, has apparently been in Mischa's life for just a short time. Mischa started dating Sebastian just this month, and went public with a night out clubbing in London about a week ago.