The Stranger Things star, who married Allen in 2020, plays a Russian super-soldier and father to Scarlett Johansson’s titular superhero in the new Marvel film.
Harbour had to lose weight through filming, as his character begins the film balding and rotund due to years in prison.
Harbour has now revealed that he and Allen went on their first date while he was initially out of shape for the role, and slowly lost weight over the course of filming and the early months of their relationship.
“It’s a true testament to my undeniable charisma when I say that my wife met me at 280 pounds with this beard and this hair,” the actor told The New York Times. “We went on a date at the Wolseley [restaurant] in London, and she really fell for me at my worst, physically and hair-wise.
“So as the thing went on, I started losing the weight and working out. And she honestly has some mixed feelings about it. Which is a good place to be in a relationship. It’s really good to start the relationship from that part, as opposed to being the young, handsome buck and watching yourself degenerate over the years.”
Harbour and Allen married at a chapel in Las Vegas last year, with Harbour recently revealing that becoming stepfather to Allen’s children has “changed [his] life”.
The actor also spoke about his struggles with alcoholism, adding that adopting a cat helped him in his journey to sobriety.
Watch: The cast of 'Black Widow' on being family and trying to speak Russian