Supposedly, Horan chose to keep the relationship a secret after he had a quick change of heart. But why keep the union private?

"Niall wants everything kept completely under the radar as he feels they simply won't survive if they're being watched," a source told Heat World, a UK magazine. "But the truth is, he's mad about her and when he's in Ireland they're spending almost every second together."

Though rumors were flying that Horan was dating singer Ellie Goulding recently, it's clear that the 1D singer only has eyes for Whelan. In fact, the couple are reportedly very close.

"She's flown out on four different occasions to meet him over in London and be close to him," the source continued. "Although they would prefer to keep the relationship quiet, they actually get to hook up together a lot more than you'd think and Zoe is a regular face backstage at their gigs."

It looks like Horan is in relationship bliss with Whelan. And the singer has the approval and support of his 1D bandmates - Zayn Malik, Harry Styles, Louis Tomlinson and Liam Payne.

"All the other lads in the band are aware of how much he likes her," the source explained, "and even though things have been on and off at times, he's always felt she was the only girl he wanted a proper relationship with."

Think Horan should declare his love for Whelan publicly? Let us know in the comments section below!