One Direction's Irish heartthrob Niall Horan has granted the birthday wish of one of his fans by recording her a personal video message.

Melena Butera, who has Down Syndrome, has been the centre of an online campaign launched by her older sister, 20-year-old Julianna, who is desperately trying to get the 'One Thing' superstars to meet her sibling.

Julianna uploaded videos of Melena singing along to One Direction's hit singles and talking about the band, and was overwhelmed to see that Horan took time out of his busy schedule to respond with a 16th birthday message for her.

In the clip, which was filmed during the group's video shoot for 'Live While We're Young', he can be heard saying: "Hi Melena, it's Niall here from One Direction. I've seen the video - it's absolutely incredible."

"Sorry we can't come to see you, you're a massive fan we know. Thank you so much for the support. All the love from the boys, bye," he concludes before blowing a kiss into the camera.

Watch the video campaign to get Melena to meet One Direction below: