The currently-untitled "The Wolverine 3" is underway with Hugh Jackman returning as the clawed mutant.
The actor said he would not appear just as a cameo, reported Aceshowbiz.
"I think what you say is true. There is a project in development. I understand that Professor Xavier will be making more than an appearance, however, and that intrigues me," Stewart said.
The actor added fuel to the speculation that the upcoming film would follow the 2008 comic book storyline "Old Man Logan", in which Wolverine was in his twilight year.
The movie will be the last one in which Jackman plays Wolverine. The actor decided to leave the franchise after portraying the character for 17 years. Directed by James Mangold, the mutant movie is slated for a release in the US on March 3, 2017.