Kate Hudson and Hugh Jackman "were a mess" after watching their new movie Song Sung Blue for the first time.

In the new biographical drama, the stars play Mike and Claire Sardina, who form the Neil Diamond tribute band Lightning & Thunder.

During an appearance on The Graham Norton Show, Hudson and Jackman revealed that they were emotional wrecks after seeing the film, as were Hudson's mother Goldie Hawn, stepfather Kurt Russell and Neil Diamond himself.

"They (Hawn and Russell) were a mess. Hugh and I were also a mess when we saw it for the first time, which is really rare. It is such an intense love story," Hudson shared, as Jackman added, "Neil rang me crying because he was so moved by the movie."

Both Hudson and Jackman also met with the Sweet Caroline singer while preparing for the film - and they both had vastly different experiences.

"It was such a lovely emotional meeting. He loves Mike and Claire and he loves the movie. He was so grateful for it, which I was not expecting," the Almost Famous actress recalled.

The Wolverine actor then shared his story, saying, "I went to meet him and actually stayed the night. It was so great, when, at dinner time, he suggested karaoke. We sang, I Dreamed a Dream from Les Mis, Can't Help Falling in Love, and Sweet Caroline. It was wonderful."

Elsewhere during the interview, the Australian actor promised host Graham Norton that the film's story is true, even if it seems "unbelievable".

"I promise, when you watch it, part of you is going to say, 'Hollywood, take it down a notch, it's already a good story,' but everything is true. It's an extraordinary story and they had an unbelievable ride," he teased.

The Greatest Showman actor also heaped praise on his co-star, calling Hudson "a force of nature" who gives "one of the best performances you will ever see".

Song Sung Blue will be released in U.S cinemas on Christmas Day, and U.K. cinemas on New Year's Day.