The actor stars in the brunette beauty’s big screen directorial debut, All We Had, about a mother (played by Katie) who struggles to make a better life for her daughter during the 2008 worldwide financial crisis. Luke has nothing but praise for Katie’s skills in front of and behind the camera, but he was left confused by her drinking habits behind the scenes.

“One day we were working together early on and she was drinking a Big Gulp, a huge soda, and she was drinking it during the scene and in between the scenes. We’re doing this scene for a couple of hours and I thought gosh, she was drinking a lot of soda,” he recalled on Tuesday night’s (06Dec) Conan. “At a certain point I said, ‘You know, you’re really drinking too much soda,’ and she just looked at me and she said, ‘Luke, I hadn’t had a soft drink for seven and a half years.’ And I said, ‘You know what, I ought to mind my own business. I think a good idea for me on the rest of this film is just let you direct me and I’ll mind my own business.’”

Host Conan O’Brien joked her previous “situation” may have meant drinking soda was banned, referring to her marriage to Scientologist and actor Tom Cruise.

Katie has also been doing press recently to promote the movie, due to hit cinemas from Friday (09Nov16), and stopped by The Tonight Show Starring Jimmy Fallon on Tuesday. The 37-year-old spoke of how she kept the cast and crew’s spirits high during the intense shoot by relying on a track by Beyonce.

“This movie it's a mother daughter story and there's a lot of high emotion,” she explained. “So you need to have some fun. So we did a lot of Drunk In Love, a lot of break dances on our set.

'We had a great time, because I've been in this business luckily for 20 years now, and I love being on a happy set...”