Passage: After X-Men: Days of Future Past (2014) erased the events of X-Men: The Last Stand (2006) from the series' timeline, Kinberg expressed interest in a new adaptation of Chris Claremont and John Byrne's "The Dark Phoenix Saga" in a future film that would be more faithful than his previous attempt with The Last Stand, which was not well received. The new adaptation was confirmed as a follow-up to Apocalypse in 2016. Kinberg signed on to make his directorial debut in June 2017, when the majority of the cast was set to return from Apocalypse. Filming began later that month in Montreal and was completed in October 2017; the entire third act was later reshot in late 2018 following poor test screenings. The film was dedicated to the memory of X-Men co-creator Stan Lee, who died on November 12, 2018.

Question: What film was this movie a follow-up to?
Apocalypse