John Travolta Praises Olivia Newton-John Amid Cancer Battle: 'I'm Very Proud of Her' (Exclusive)

The actor opened up to ET at the premiere of his new film 'The Fanatic' in Hollywood on Thursday.

John Travolta is sharing some super sweet words for his longtime friend Olivia Newton-John amid her ongoing public battle with stage 4 cancer.

The celebrated star walked the red carpet at the premiere of his new film, The Fanatic, at the Egyptian Theatre in Hollywood on Thursday, and he stopped to talk with ET where he had nothing but praise for his beloved Grease co-star.

"She looks incredible," Travolta, 65, marveled. "She doesn't look any different than [she did] years ago, and I'm very proud of her."

"I'm very happy about Olivia," the actor added with a smile.

Newton-John, 70, sat down with 60 Minutes Australia, in an emotional interview that aired earlier this month, where she opened up about her latest battle with cancer and explained that she's working hard to enjoy life to the fullest.

ET spoke with Newton-John last week, and the actress shared, "I just want everyone to know, I'm here, I'm doing great. I'm doing really well and I'm really healthy."

Travolta and Newton-John have long been close friends and fans of one another -- but in Travolta's new film, The Fanatic, the actor shows a different, darker side of fandom.

In the movie, Travolta plays a man named Moose who is obsessed with an actor and increasingly begins to encroach on the star's space. The role required something of a radical transformation that included a bizarre, bowl-cut hairstyle and a truly strange overall look.

"I found on the internet this guy that had that haircut and rimless glasses and I superimposed it on a photograph [of me] and I sent it to [director] Fred Durst, and he fell in love with the look," Travolta explained. "Then we added the Hawaiian shirt and the shorts and it just came together, [as] kismet, you know?"

Travolta said that, when it comes to dedicated fans, he's had some good experiences and he even knows exactly who his biggest fan really is.

"My number one fan in the world is Sharon Travolta," the actor said, referring to a devoted admirer who lives in England and who's been a follower of the actor's work for decades. "She changed her name to my name out of love 40 years ago and on her birthday she watches every movie [of mine] 24/7, and that's kind of her gift to herself and me on her birthday."

The actors' die-hard devotee will soon have another movie to add to her list with The Fanatic, which hits theaters Aug. 30.