"I guess it's bittersweet, I don't know," Williams told ET at D23 Expo, where Disney and Lucasfilm presented new footage from the saga's ninth episode. "It's a wonderful experience, I didn't expect it."
Asked if he believes Rise of Skywalker is the "last one," Williams admitted, "I have no idea, but it'll probably go on for another 40 years."
Williams then said the presence of late original trilogy co-star Carrie Fisher — who will reprise her role as General Leia Organa through the use of repurposed footage captured by writer-director J.J. Abrams on The Force Awakens — is "very special," but Williams knows little about the special effects process making that return possible. "I don't know much about what's going on," he said.
During his onstage appearance at D23 Saturday, Abrams said his Episode IX "needed" Fisher's Leia, mother of the corrupted Ben Solo, a.k.a. Kylo Ren (Adam Driver).
"The character of Leia is really the heart of this story. We realized we could not possibly tell this story without Leia," Abrams said. "We had footage from Episode VII that we could use in a new way. So, we were able to use Carrie in a new way."
Rise of Skywalker will mark the final appearance for some characters, but others could continue on beyond the Skywalker Saga and resurface elsewhere in the Star Wars galaxy.
"We're using this appropriate time as an opportunity to see where we're going now that we're leaving the Skywalker Saga behind," Lucasfilm president Kathleen Kennedy previously told MTV News. "But there's no question that there's certain characters that we've created certainly in the last three movies that we may very well wanna see down the line in the future."
Starring Daisy Ridley, John Boyega, Oscar Isaac, Adam Driver, Kelly Marie Tran, Anthony Daniels, Keri Russell, Richard E. Grant, Naomi Ackie, Domhnall Gleeson, Joonas Suotamo, Ian McDiarmid, Billy Dee Williams, Carrie Fisher, and Mark Hamill, Star Wars: The Rise of Skywalker opens December 20.