The introductions happened behind the scenes at "Saturday Night Live," where Fallon, 45, was a cast member from 1998 until 2004. Juvonen accompanied close pal Drew Barrymore, who was hosting the show that week, to the set.
"I kind of crept in quietly, and all of a sudden Jimmy goes, 'Hey, Nancy! You're Nancy? Hi, it’s so nice to meet you, welcome!'" Juvonen, 52, recalled. "And I felt just so embraced and cool, like, ‘Thank you! Thank you for welcoming me in. This is so nice, it’s so intimidating (here).'"
But the sparks really flew when the pair met again on the set of Fallon and Barrymore's 2005 rom-com "Fever Pitch," which Barrymore and Juvonen helped produce with Flower Films, the production company they co-founded.
"Then on the set (of 'Fever Pitch'), we were on location and that really creates this camp feel for everybody. And he was just so friendly and fun and welcoming and he loved music," shared Juvonen.
"When I really developed a crush was when (co-producer) Bradley Thomas' kids came to set," she revealed, adding that watching Fallon's easy way with the children made her fall for him completely.
"I played with Lucy and Jimmy played with Charlie — really played, really into it, as if they’d come to visit us,” she shared. “So, I think that’s when my heart just sort of melted even more."
At the same time, Fallon was also crushing hard.
"I remember when I first experienced the magic that is Nancy Juvonen," Fallon said, describing the first day of filming as a "rainy, gray” day in Boston.
"You walked to set and I want to say you had on white pants, a pink sweater and a green backpack ... and blonde hair and your white teeth," he sweetly recalled. "You just stood out in this gray — it was almost like a painting. You stood out like neon."
"And I was like, 'Wow.' Yeah, you just stuck out. And you were just so fun — we had so much fun, didn’t we?” he added.
After months of flirting on set, the two met up again in London and began dating. The happy couple tied the knot in December 2007 and are now parents to two adorable daughters, Winnie, 6, and Franny, 5, who've been a big help to their dad as he continues filming "The Tonight Show" from home.
Watch Jimmy and Nancy share their sweet story in the video above!