Milo Ventimiglia shares 'vows' he made with Mandy Moore before 'This Is Us' started

Mandy Moore and Milo Ventimiglia have played Rebecca and Jack Pearson, respectively, on NBC's This Is Us since its 2016 debut.

In the show, they exchanged real vows and became one of television's most beloved married couples.

But before the mania began, Moore and Ventimiglia made a real-life pact to each other.

"Right before the show premiered, we were in New York for the upfronts, the big advertiser conference, and everybody was kind of milling about," Ventimiglia explained on The Tonight Show Starring Jimmy Fallon on Tuesday. "Mandy and I were just, like, off to the side by ourselves, and we just kind of raised our glasses to one another."

"We almost took vows with one another, where it was like, 'Hey, I promise to always communicate. I promise to not be happy until you're happy. I will always look out for you,' and all that," the three-time Emmy nominee continued. "And we have stayed very true to what we said in the beginning. I mean, I gotta say, she has been probably in my 26 years in front of the camera the best partner I've ever had. Her commitment, her dedication, her growth as an artist."

This Is Us premiered its sixth and final season Tuesday night.

Watch Ventimiglia's Tonight Show appearance as well as the This Is Us trailer below.