One Direction took the stage in Stockholm, Sweden for their Take Me Home tour on May 8, where they paid tribute to a man who's a Swedish national treasure: Max Martin, writer and producer of some of the best pop songs ever recorded. He's the man behind the Backstreet Boys' 'I Want It That Way,' and 1D delivered an impromptu performance of the tune live.

The video of their brief cover made its way to BSB themselves, who were honored and impressed by the on-the-spot rendition of what became their signature song. The Backstreet Boys took to Twitter to express their appreciation and extend their compliments to the British boy band:

1D may have just been returning Backstreet's favor -- NKOTBSB covered 'What Makes You Beautiful' live last year!