Sienna Miller and Mischa Barton were out earlier today to help their pal Matthew Williamson launch his new collection for H&M in London. Fresh from a quick trip to Germany, Sienna sipped champagne and posed for photos while Mischa stayed busy checking out the merchandise. Sienna and Matthew have always been just friends, but she's recently been linked romantically to musician Marcus Foster. Even though we haven't seen her with Balthazar in a few months, we wouldn't count him out of Sienna's love life just yet.
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