Mark Hamill pays tribute to Carrie Fisher ahead of 'Star Wars IX'

July 30 (UPI) -- Mark Hamill paid tribute to the late Carrie Fisher on Twitter as production is set to start on Star Wars: Episode IX.

"It's bittersweet facing my final chapter without her-She is simply irreplaceable," Hamill said on Sunday alongside photos of himself with the actress on the set of Star Wars: The Last Jedi and during filming of the original Star Wars trilogy.

"I'm finding solace in the fact that she won't BE replaced & would love the worldwide outpouring of affection from those who loved her when they heard the news. #CarrieOnForever," he continued.

Hamill and Fisher appeared in the Star Wars series as brother and sister Luke Skywalker and Princess Leia, respectively. The pair were last seen together in 2017's The Last Jedi, which was released after Fisher died in December 2016 following a heart attack.

Disney and Lucasfilm recently announced that Hamill and Fisher would be returning for the next entry in the Star Wars saga, Episode IX, which begins production on Wednesday. The film is set for release in December 2019.

"We desperately loved Carrie Fisher. Finding a truly satisfying conclusion to the Skywalker saga without her eluded us. We were never going to recast, or use a CG character. With the support and blessing from her daughter, Billie (Lourd,) we have found a way to honor Carrie's legacy and role as Leia in Episode IX by using unseen footage we shot together in Episode VII," Episode IX director J.J. Abrams said of how Fisher will appear in the new film.