When making the announcement, he was flanked by co-star Hugh Jackman and director/co-author James Mangold.
"It's only been a few days; I was watching the world premiere in Berlin exactly a week ago that sitting beside Hugh watching him say goodbye I realized there would be no more perfect time to say au revoir, adios, goodbye to this franchise than this; I'm very content," Stewart said during the interview.
Stewart added it was an epiphany for him, and at no one time did he give it a thought that it would be his last appearance. He noted Jean Grey had already vaporized his character. He said toward the end of the film; they were three or four in the room when mechanical monsters burst in and wanted to devour them. So instead of being eaten alive, he was vaporized, ending his character on the set.
Stewart wasn't the only one to announce his departure from X-Men. Jackman also reconfirmed on the same show that "Logan" would be his last appearance as Wolverine.
Stewart had previously left his future as Professor Charles Xavier up in the air, throwing out tongue-in-cheek hints that he could reprise the role for Deadpool 2 or other future X-Men films.
This new announcement, though, ends any speculation that the 76 year- old Actor will take part in any future X-men movies.