Believe it or not, the two were an item for a few months back in 2014 -- and nearly four years later, the Riverdale star is inspiring Carter's new music!
ET's Katie Krause sat down with the 30-year-old singer for a Facebook Live interview in Los Angeles on Wednesday, where he spilled all about their brief romance, and what she thinks of his new song, "Seattle Tide."
"She was working at Republic of Pie. [I] saw her with her little red curls and I asked her out on a date. I was very gentleman-like with her," Carter revealed. "We dated for five or six months, something like that, and then we stopped dating."
According to Carter, Petsch has heard "Seattle Tide" -- which he wrote after bumping into her at an airport in Seattle after their breakup -- and instantly knew the song was about her when he played it for her "in person." And while the 23-year-old actress is now dating Travis Mill, Carter couldn't be happier for her. "I have not been watching [Riverdale], but I heard it's doing great. I'm very happy for her," Carter shared. "She's a very talented actress."
During his interview with ET, the singer also opened up about other inspirations behind his new album, Love, which drops on Friday. His song, "Champion," was written about his late father, Robert, who died at 65 in May 2017.
"It was so tough writing that song," Carter confessed. "He was a professional boat racer, and he never lost a race, so I call the song 'Champion.'"
"When I was, like, four years old, I drowned in a swimming pool and I died, and he saved my life... I remember going through, like, this very vivid experience and seeing some sort of afterlife or something," he continued, explaining some of the song's lyrics. "He was a very instrumental person in my life. He was a very good rock for me."
After his father's death, Carter said he and his family "unfortunately" didn't come together. "The dynamic of my family is like in its own category. It's very strange," he explained, adding that his and his siblings' early success tore his family apart. "Money coming in so fast and not growing up with money... I really saw the industry kind of tear apart my family, being in the news and stuff like that. Sometimes it's really sad to think about."
These days, however, he and his Backstreet Boy brother Nick don't talk much about headlines. "I think it's just part of our routine, our life, that Nick and I never really talk about anything to do with the business. Like, nothing."
As for what inspired the title of his new album, Love, Carter said he's never actually been in love.
"When I came up with the concept of the album, I went and got [love] tattooed on my neck, but it was when I was going through a really bad breakup. I did it out of spite or some stupid reason," said the former child star, who plans to remove the ink. "[Getting it removed] probably won't hurt as bad as the relationships did."
"I think I might have been in lust and co-dependent and all of those things, but not really, truly in love," he expressed. "I question love heavily these days... The outcome is always disappointment."