"Production hasn't even started yet," the source says, shooting down rumors that Cruise has tapped the 28-year-old actress as wife No. 4.
Kirby has landed a role in Cruise's upcoming Mission: Impossible 6, which begins filming next month in Paris -- though according to In Touch, Cruise has been a big fan of the British actress since seeing her in Netflix's The Crown.
While ET's source slammed reports that the two are dating, Cruise definitely has a history of romancing his co-stars.
The 54-year-old actor met his second wife, Nicole Kidman, on the 1990 set of their film, Days of Thunder, shortly after he divorced his first wife, actress Mimi Rogers. Ten years after Cruise and Kidman's split, the actor began a three-year relationship with his Vanilla Sky co-star Penelope Cruz.
Though Cruise hasn't been seen in a serious relationship with anyone since his 2012 divorce from Katie Holmes, outlets have continued to link the father of three with those on his movie sets -- Laura Prepon in 2014, Sofia Boutella and Emily Thomas in 2015, and Annabelle Wallis in 2016.
As for Kirby, the blonde beauty most recently dated Douglas Booth from 2011 to 2013, and as of January, told outlets that she was single.
Regardless of their romantic lives (or lack thereof) Cruise and Kirby will put their game faces on when M:I 6 starts filming on April 10.
"It starts in a very unconventional way," director Christopher McQuarrie teased on the Empire Podcast. "It does not start with action. That was the hardest pitch of this movie."
"I've seen five of these movies and I don’t know who Ethan Hunt is. One movie sort of dealt with his personal life; the other movies are about people speculating what’s really going on in Ethan’s head. I want to know who Ethan is in this movie, I want an emotional journey for this character, and Tom really embraced it," he added.