One Direction's Niall Horan has admitted that despite rising to an international level of fame since appearing on The X Factor he still gets starstruck and there's one celebrity in particular he has a real soft spot for.

In a new interview with Digital Spy, the heartthrob explained that he gets nervous around certain people and songstress Katy Perry sets his heart racing:

"I was starstruck by Michelle Obama. She's an amazing-looking lady, and I'm a massive Barack Obama fan anyway. Katy Perry still gets me every time. She's very funny in person! We met at the Teen Choice Awards and she pulled my cheeks apart and told me how cute I was. My life was literally flashing before my eyes!"

Although the lads are currently in the USA on their debut stateside headlining tour, Horan opened up about the progress of their new album and revealed that Tom from McFly has penned a track for the group and they will team up with singer-songwriter Ed Sheeran once their American dates are over:

"Tom from McFly has just written a song for us and it's very, very good! He wrote a song on the last album too and we love his style. We've got another writing session with him soon which should be fun. We're also working with Ed Sheeran again - when we get back from America it's straight to the studio with him!"

Watch behind-the-scenes footage from One Direction's 'Up All Night' DVD below: