They enjoyed a string of dates back in 2014 but decided they were better off as friends.
And Niall Horan revealed he still holds a candle for his ex-girlfriend Ellie Goulding during an appearance on The Ellen DeGeneres Show on Wednesday.
The 23-year-old star took part in a quick-fire game of Who'd You Rather with chat show host Ellen, and ended up picking the Burn singer as his dream date.
Explaining the rules, Ellie told Niall: "You're single. I'm going to try and find you the perfect girlfriend. We're going to play a speed round of Who'd You Rather?
"I'm going to show you two pictures and you're going to choose one [person] over the other."
While he selected both Rihanna and Selena Gomez on three occasions each, beating the likes of Taylor Swift and Demi Lovato, it was Ellie he eventually settled on as his ideal woman.
He selected the British beauty over Rita Ora, Jennifer Lopez and Kendall Jenner.
The game also revealed Niall has a penchant for an older lady, choosing Diane Keaton, 70, and Demi Moore, 53.
Ellen declared: "I think Ellie's the winner! You wana be with Ellie. It's official. If Ellie's watching, there's your guy!"
During the interview, which marked Niall's first solo visit to The Ellen DeGeneres Show without his One Direction bandmates, the pair chatted about how they both look alike and compared photos of themselves.
Joking about how often he gets compared to Ellen, Niall laughed: "Every day of my life. I don't mind it though, I like it!"
He also talks about writing his debut solo single This Town, before treating the studio audience to a live performance.
Ellie and Niall are alleged to have hooked up in 2014, while she was supposedly seeing Ed Sheeran.
The 29-year-old is still plagued by the rumours she cheated with the Irishman on then-'boyfriend' Ed Sheeran, despite her insistence she never dated the Thinking Out Loud singer.
Sheeran's song Don't, which is about a lover who cheated with his friend, was rumoured to be about Goulding; her song On My Mind, which tells of a one-night stand with a tattooed admirer who got too attached, was rumoured to be her reply.
However, Sheeran has never confirmed who the song is about, while Goulding has persistently denied her part.
Ellie recently confessed she's still a great admirer of the former 1D singer.
"We're still friends. We went on a few dates, and it was really fun. He's a really, really lovely guy,", she told Seventeen magazine.
"He's got the biggest sense of humour, he's very caring, and I see him as a genuine friend in the industry."