Britney Spears and Sam Asghari have made their red carpet debut as a couple, more than two years into their relationship. The 37-year-old singer and 25-year-old model and personal trainer attended the Los Angeles premiere of "Once Upon a Time in Hollywood" Monday at the TCL Chinese Theatre. Spears wore a formfitting red dress with black sandals, while Asghari sported a a cream-colored suit, white shirt and black tie. Asghari kept an arm around Spears as they posed for photos. In addition, E! News said Spears sparked engagement rumors by wearing a diamond ring on her left hand. Spears and Asghari celebrated their red carpet debut as a couple on Instagram. "Our first premiere," Spears captioned a pair of photos. "My beautiful date," Asghari responded in the comments. Spears and Asghari met on the set of Spears' "Slumber Party" music video, which debuted in November 2016. Spears marked their one-year anniversary as a couple in an Instagram post in February 2018. "I've been with this man for over a year... everyday he inspires me to be a better person and that makes me feel like the luckiest girl in the world!" she wrote at the time. Spears and Asghari's appearance follows news of Spears' indefinite hiatus from work and reports she was treated at mental health facility in April. "Sam has stuck by her side throughout all of her recent struggles and knows that this is just a phase in Britney's life that they will have to adjust to right now," a source previously told E! News. "Once Upon a Time in Hollywood" is directed by Quentin Tarantino and stars Brad Pitt, Leonardo DiCaprio and Margot Robbie. The movie opens in theaters Friday.