Katy Perry gets in on One Direction love, tweets her congratulations

Katy Perry is the latest celebrity to join in congratulating One Direction on their US success.

Katy, who was a guest judge on X Factor during Niall Horan's first audition, tweeted the One Direction cutie saying: "congratulations, you didn't let me down! xo"

[Related article: Gary Barlow congratulates One Direction]

[Related article: One Direction appear on Today show]

Aw! Niall was obviously chuffed that the singer had contacted him, and he replied saying: "hey katy,thank you,let's hope it holds out this week!Thank you for putting me thru!we've been working hard,I won't let you down" [sic]

One Direction performed on the Today show ahead of their album release / WENNOne Direction performed What Makes you Beautiful on America's Today show earlier in the week, and have seen their album storm the US charts as a result.

Their debut album, Up All Night, is now sitting at number one in the US iTunes chart, with the deluxe edition at number two, despite only being released on Monday.

The boys are curently at the top of the US album charts / WENNIn fact, US Directioners have now become so obsessed with Harry, Liam, Niall, Louis and Zayn that police had to be called to their New York hotel last night after fans mobbed them.

We love that 1D mania is well and truly spreading.

One Direction - One Thing - Behind the Scenes by news-de-stars