Austin Butler was hospitalised immediately after filming Elvis.
The 30-year-old actor stars as the late King of Rock and Roll in the new biopic and reportedly ended up bedridden with symptoms of appendicitis once filming was complete, according to EW.
He said: "It was all-consuming. Then my body just said, 'All right, I need to rest' [and I went to the hospital]."
The Once Upon a Time in Hollywood star - who lost his mother Lori to cancer in 2014 - then went on to reveal that he felt a "connection" with Elvis Presley because he had also lost his mother Gladys to the disease back in 1958.
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The Hound Dog hitmaker and Butler also both lost their mothers at the young age of 23.
He told EW: "That was one of the first keys that connected me to him on a very human level rather than the idea of Elvis. Learning how close he was with his mom, because my mom was my best friend, I could connect to him on that level of grief."
Butler explained that since completing the movie, he feels as if the Hound Dog hitmaker - who died of heart disease at the age of 42 back in 1977 - is now a "close friend" to him and spoke of how he wanted to make Elvis's former wife Priscilla "proud" with his performance.
He said: "Elvis now this really close friend that I can come back to, and I always get joy in his presence. I'll pop on his music or watch one of his films. It'll always be a close part of my life. I wanted to make Priscilla proud and do justice to her and her family."
The former The Carrie Diaries star finds it "sad" that Elvis never got to tour the world - doing his only international show in Canada - despite being one of the most famous performers and loved across the world.
Butler shared: "The sad bit about it is that Elvis never got to tour the world. That is a thing that I think a lot of people don't quite realise.
"And that was a big thing that he really wanted to do."