It was a day of celebration for Mila Kunis and Ashton Kutcher. Kutcher, 35, joined Kunis, 30, in St. Petersburg, Fla., on Saturday to attend her brother’s wedding. Michael Kunis, 36, tied the knot with ballet dancer Alexandra Blacker, 29, who trained Mila to play a ballerina in 2010’s Black Swan, at the Cathedral Church of Saint Peter. The couple got engaged last December in San Diego. Following the ceremony, to which Mila wore a blush, knee-length dress, a reception was held at the historic St. Petersburg Yacht Club. According to a source, Mila and Ashton's present to the newlyweds is their upcoming »