Horan publicly voiced his approval as the 25-year-old was interviewed by Eamonn Holmes and Ruth Langsford to promote her character Mitzeee Minniver's upcoming exit storyline.
[Rachel Shenton on This Morning today.]
Writing on Twitter, Horan enthused: "That girl on @itvthismorning is beautiful!"
That girl on @itvthismorning is beautiful !— Niall Horan (@NiallOfficial) February 8, 2013
Later in the show, Holmes told viewers: "Niall from One Direction has been in touch, commenting on our last guest, saying how striking she was."
Langsford added: "And she's single Niall, I've checked for you! That's all I'm saying!"
After learning of the popstar's tweet, Shenton joined forces with This Morning's Hub presenter Matt Johnson to send a photo and message to the 19-year-old. Horan then replied with a photo of his own.
Shenton bows out from Hollyoaks next Friday (February 15) after two and a half years in the role of fan favourite Mitzeee.
Her exit storyline includes a cameo appearance from This Morning's Holmes as Mitzeee is interviewed on his Sky News breakfast show.
New! Digital Spy Soap Scoop video - watch Amie Parker-Williams reveal the biggest storylines on the way in Coronation Street, EastEnders, Emmerdale and Hollyoaks next week.