The Teenage Dream superstar sent a tweet to boyband member Niall Horan after their album Up All Night soared to number one on the US iTunes chart during its first day on sale.
The standard and deluxe editions of the record currently hold the number one and two positions respectively.
© Rex Features / DUPUY FLORENT/SIPA/Rex Features
© Rex Features / Copetti/Photofab
Perry - who guest judged the X Factor auditions in Ireland when Horan went through - wrote to the singer: "congratulations, you didn't let me down! xo"
Horan responded gratefully: "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"
One Direction yesterday made an appearance on the US breakfast programme The Today Show to promote the LP.
Watch the group performing 'What Makes You Beautiful' below:
