Mark Hamill 'Can't Watch' Luke's Goodbye to Carrie Fisher's Leia in 'Star Wars: The Last Jedi' (Exclusive)

The 'Star Wars' icon opened up to ET about his emotional final scene with his long-time friend, and how watching now, after Fisher's death, is just too hard.

In Star Wars: The Last Jedi, Luke Skywalker is reunited with his sister, Princess Leia Organa, for a deeply touching scene that was one of the emotional highlights of the action-packed sci-fi epic.

As it turns out, the scene was nearly as emotional for stars Mark Hamill and Carrie Fisher, who shared the screen for the first time as their characters since Star Wars: Return of the Jedi in 1983. 

The 66-year-old actor sat down with ET's Ash Crossan and opened up about the delicate scene, which saw Luke sweetly kiss his estranged sister -- now general of the Resistance -- on the forehead, and how the gesture came about organically.

"I didn't decide it and say, 'Can I do this?' I mean, in the take -- I don't know if we rehearsed it or not, but it just happened," Hamill recalled. "I was standing up and they weren't ready for it. They said, 'No, do that again.' And we did it for a second take, and like I said, it was just spontaneous."

Hamill explained that now, in light of Fisher's untimely death, the scene was "really momentous" for him at the time, because Luke "was saying goodbye to his sister forever," and soon after Hamill had to say goodbye to Fisher as well.

"I can't watch that scene. It's just, you know, takes me out of the movie completely," he shared. "I'll get over it, but she'll be forever missed and she's irreplaceable."

Fisher died in December 2016 after a brief hospitalization following a heart attack. In the days following Fisher's death, Hamill paid an emotional tribute to the icon, sharing, "It's never easy to lose such a vital, irreplaceable member of the family, but this is downright heartbreaking."

"She was OUR Princess, damn it, & the actress who played her blurred into one gorgeous, fiercely independent & ferociously funny, take-charge woman who took our collective breath away, determined & tough, but with a vulnerability that made you root for her & want her to succeed & be happy… I am grateful for the laughter, the wisdom, the kindness & even the bratty, self-indulgent crap my beloved space-twin gave me through the years," Hamill continued. "Thanks, Carrie. I love you."

Earlier this month, Hamill received a star on the Hollywood Walk of Fame, where he was joined by Star Wars co-star Harrison Ford, the franchise's creator, George Lucas, as well Fisher's daughter, Billie Lourd, who also appeared in both Star Wars: The Force Awakens and The Last Jedi as Lieutenant Connix, a member of the Resistance.

"I see so much of Carrie in Billie," Hamill told ET at the ceremony. "I adore her. She's my pretend space niece, since her mom was my pretend space sister… I'm very protective of her."

Check out the video below to hear more.

Star Wars: The Last Jedi is available on digital now and on Blu-ray Mar. 27.