Meanwhile, Sam looked smart in a cream suit, white shirt, black tie and suede black boots.At a movie premiere with Hollywood’s heaviest hitters (Leonardo DiCaprio, Margot Robbie, and Brad Pitt), all eyes were on music’s queen, Britney Spears — and for good reason. On Monday night, the pop star walked her first red carpet with longtime boyfriend Sam Asghari at the Once Upon a Time in Hollywood screening in Los Angeles.