Jude Law and Sienna Miller

"I'm the happiest girl alive," Sienna Miller, 23, declared from her London doorstep on Jan. 5. And why shouldn't she be? The actress is set to marry PEOPLE's Sexiest Man Alive, Jude Law, 32, who popped the question on Christmas Day with a big rock: nine diamonds in a platinum circle set in gold. The two, who met on the Alfie set in 2003, haven't picked a date yet, but Miller says, "I'm ecstatic.