Sir Patrick Stewart keeps a bag of James McAvoy's hair in a safe at his home, the actor revealed.
James, who plays the younger version of Sir Patrick's Professor Charles Xavier in the X-Men franchise, confessed that he found the keepsake "kind of creepy" as he spoke on The Graham Norton Show about finally going bald for the new Apocalypse film.
He said: "I shaved (my head) months before to see what it would look like and turned up on the shoot with about two months' growth and they were like, 'What have you done?' and I had to have the first of 17-hour hair extensions sessions.
"When we finally shaved it off we decided to facetime Patrick Stewart so he could pass on the baldy baton.
"We though it was funny when he asked if he could have some of the hair, but it turns out the director bagged it up for him and he now has all my hair at home in a safe, which is kind of creepy."
James, 37, also said he would be on board to make more X-Men films.
He said: "If they write good stuff for us, if schedules work out and they pay enough money I am sure we'll still keep doing it."
X-Men: Apocalypse is released in the UK on May 18.
The Graham Norton Show airs on May 13 on BBC One at 10.35pm.