Jennifer and Nicholas got together on the set of X-Men: First Class in 2010 and dated on-and-off until 2014, right around the time when X-Men: Days of Future Past wrapped. Since then, the two have had to work together on X-Men: Apocalypse, which released in 2016, and Dark Phoenix, which came out in 2019. Luckily, their characters, Beast and Mystique, didn't have too many intimate scenes.
During a January 2019 interview with Evening Standard, Nicholas said that working with Jennifer post-breakup wasn't at all weird. "It's pretty similar to Skins," he said, referring to the show he starred at the beginning of his career. "We're a big family. We've been doing those movies since we were 20 years old. As much as the Skins crowd grew up together, the X-Men crowd really grew up together. It's been a good eight, nine years making those movies. We've all got to get along. We've all got to have fun."