When Stewart was to play Charles Xavier for the first time back in 2000, he didn’t even know who the X-Men were (as he describes elsewhere in his book). In 2016, having played the part in six movies, Stewart admitted that he didn’t want to play Charles Xavier yet again in 2016, but he was lured by an opportunity to work with James Mangold, a director he admired. He also liked the new premise of the script, writing:
“I started reading. Whoa. The year is 2029. The X-Men themselves are in steep decline, and no mutants have been born for twenty-five years. James and his co-writers, Scott Frank and Michael Green, were exploring the idea of superhero entropy — what happens when they get clapped out and old, their powers waning, the general public indifferent to them?”
Charles, in addition to living in a tank, is dealing from dementia. He babbles, misremembers things, and occasionally has superpowered mental aneurysms that unwittingly cause earthquakes and bodily damage. Filming with his co-stars was also a wonderful experience for Stewart, not just with Jackman, but with the young Dafne Keen, who plays a character named Laura, a semi-feral mutant child with Wolverine’s powers. Stewart admired the 11-year-old’s passion, writing:
“We started filming in May 2016. Being back on a set with Hugh was thrilling and invigorating. We were joined by Stephen Merchant as the mutant Caliban … and child actress Dafne Keen, the most extraordinary juvenile performer with whom I have ever worked. […] Dafne’s focus and seriousness were something to behold when we were rehearsing and shooting — she reminded me of myself in my younger ‘We are not here to have fun’ days.”
Stewart said, though, that when the cameras stopped rolling, Keen became kind and genial.