[custom_adv] The film, which stars Leonardo DiCaprio, Brad Pitt and Margot Robbie, is directed by Quentin Tarintino and explores Hollywood in 1969 - the 'golden age'. [custom_adv] The mum-of-two wore a red Nookie mini dress, black chunky heels and a silver choker for the red carpet appearance, with her hair tied up into a ponytail. Meanwhile, her boyfriend looked smart in a light-coloured suit, dark shoes and a black tie. [custom_adv] The 90's pop legend looked youthful as she stunned in a fitted red dress, with shoulder strap and cut out detailing. [custom_adv] Britney teamed the look with a pair of chunky black platform heels, a silver choker and swept her long blonde hair into a ponytail for the event. [custom_adv] 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. [custom_adv] It's a relationship milestone worth celebrating, and they did just that on Instagram (their love's natural habitat). "Our first premiere," Britney captioned two shots of the happy couple posing together at the star-studded event. Asghari commented: "My beautiful date." [custom_adv] Britney Spears made a surprise appearance at the Once Upon A Time in Hollywood premiere Monday night, and she had a special guest join her — boyfriend Sam Asghari! [custom_adv] The appearance marks the couple’s first premiere appearance together, though they were photographed together at last year’s GLAAD Awards when Spears accepted the Vanguard Award, Asghari skipped the red carpet. [custom_adv] On Monday, Spears wore a stunning red mini dress with a tiny cutout in the middle, topping off the look with a glittery silver choker necklace, chunky black heels, and her long blonde tresses in a glamorous up-do. Asghari wore a handsome beige suit with a skinny black tie.