Niall Horan of One Direction just told the world he was single, but is he lying?! Quite possibly!

Horan was rumored to be dating U.K. 'Made in Chelsea' starlet Louise Thompson back in May, but those rumors fizzled quickly. However, the whispers are growing louder as Thompson and Horan are reported to be growing hotter for one another!

Sources told the Daily Mail that Thompson broke her ex's heart to be with the Irish-born boy bander -- and that they've been sneaking around to make sure no one knows. (Whoops, looks like they're not doing so great at that part!)

"Louise has been dating Niall -- they've seen each other lots and talk all the time," an insider dished. "But it suited both of them for their nights together to be secret. He'll sneak her into his house in North London, often when it's dark. She makes sure she doesn't do anything around Chelsea to try and keep the romance away from the prying eyes of her co-stars on the show."

"Louise always insisted to Andy that she was just friends with Niall and that she;d only spent one night at his house and it was completely innocent. Foolishly, he believed her because he was madly in love," the source said. "But he's now aware of the fact Louise and Niall are in a passionate physical relationship and have been together on numerous occasions."

Ruh roh! Sounds like this hot and heavy couple may as well go public.