Katy Perry has admitted her surprise at seeing her new single reach No.1 in the States.

The singer recently released the track 'Dark Horse' as the second cut from her 2013 album 'Prism' and it has just reached No.1 on the Billboard Hot 100.

It has given Perry her ninth No.1 single in the US and speaking to Billboard, she admitted that it is probably her most different chart-topper yet.

Referring to the Juicy J collaboration, the 'Unconditionally' star said: "This No.1 is the most unexpected one I've ever had. 'Dark Horse' has been a dark horse of a song, since August when the KatyCats voted to release it early on iTunes, before 'PRISM' even came out. I'm so thrilled and grateful to have these moments."

Perry meanwhile is currently tied with five others in tenth place in the list of artists with the most US No.1 singles.

The Beatles lead with 20, with Mariah Carey (18) and Michael Jackson/Rihanna (13) following.