Ethan Slater is "unendingly proud" of his girlfriend Ariana Grande

Ethan, 32, told Us Weekly: "I'm unbelievably proud of her. She worked so hard. She and [co-star] Cynthia [Erivo] worked so unbelievably hard to not only make this movie and be the best versions of [characters] Glinda and Elphaba, but to promote it. They're incredible. I'm unendingly proud."

The actor's romance with Ariana came as his marriage to wife Lilly Jay - mother of his young son - broke down and he previously admitted he went through some huge changes as he dealt with his personal life becoming public.

He told GQ magazine: "Obviously, it was a really super big year. I think there was something that was really difficult about things in your private life being commented on and looked at by the public.

"There were a lot of big changes in private lives that were really happening, so it's really hard to see people who don't know anything about what's happening commenting on it and speculating, and then getting things wrong about the people you love.

"So just to address that part of it, that feels really hard."

He added: "But, of course, it was an amazing year and a really beautiful thing, and I'm just really excited."

During the interview with Us Weekly, Ethan went on to reveal fans of 'Wicked' have a lot to look forward to ahead of the release of part two next year.

He said: "I think people have seen already how Ariana and Cynthia have given such emotional depth to their characters and Ari in particular; her comedy is so good, and yet there's a real truth and grounding to it.

"I think what might surprise people is how far that goes in such a beautiful way. I haven't gotten to see it yet, so I'm just remembering from what I saw on the day [we filmed]. But on the day, it was really special to witness."