The two stars met while trying out for the roles that made them famous — Gabriella and Troy from Disney's "High School Musical" — and they hit it off instantly.
"I was a baby," Hudgens told The Hollywood Reporter's "Awards Chatter" podcast of those 2004 auditions. "I was 15 years old. I was like, "Oh, my God! This guy's so cute.'"
She said that detail "definitely helped the chemistry."
"I feel like we kind of created a bond right from the start," the now-30-year-old added. "It started off really organically."
By 2005, they were dating, and by the time the first film in the franchise hit the Disney Channel the following year, they were popular on a scale they'd never imagined before.
"I could not have been more grateful to have that relationship at that time, because ... we kind of blew up," Hudgens continued. "It was this massive phenomenon all of a sudden and eyes were on me. It’s just a really weird, foreign thing to go through, and by being in a relationship, I feel like it kind of kept me stabilized and grounded. I had someone to lean on who was going through it as well."
Which isn't to say that their young love was always picture-perfect.
"Yeah, of course, everything is not always the happy and dandy," she explained. "I remember one time we did have a fight, and it was while we were at rehearsals."
"High School Musical" director Kenny Ortega took notice of it, too.
Hudgens recalls him "coming around the corner with the most concerned look on his face, like, 'Oh, no! Is our movie going to fall apart right now?!'"
But there wasn't any reason for him to worry about the song-and-dance film — or any of its sequels. Hudgens and Efron may have been teens, but they were both professionals and older than their years when it came to being capable of compartmentalizing any off-screen drama.
"So I was like, 'That (argument) aside, we are just going to move forward and do what we need to do,' and we sorted it all out," Hudgens revealed.
In fact, rather than causing a problem, their romance provided an important sense of support for Hudgens during such a whirlwind time in her life.
"I think because I was so young, having that relationship really stabilized me," she said.
The couple wrapped up their on-screen partnership with "High School Musical 3" in 2008 but remained together until their amicable split two years later.