The Source Code actress credited her husband Peter White with saving her life after he noticed a suspicious-looking mole.
"I had a mole on the back of my calf, and he was adamant that I get it checked," Monaghan told Health. "I finally went, and it was skin cancer. I had quite the chunk taken out of my leg. I'm so grateful he noticed it."
She went on to joke that he has made her sensitive about any other imperfections.
"I clearly now realise he has a keen eye and wonder what other imperfections he's noticing!" Monaghan said.
Monaghan can be seen in Machine Gun Preacher opposite Gerard Butler.
Machine Gun Preacher was previously released in the US, and opens in cinemas in the UK on November 18.
Watch the trailer for Machine Gun Preacher below:
> Source Code: The movie make-up of Jake Gyllenhaal's thriller
> What is the Source Code? Exclusive video featurette