Niall Horan thinks Olly Murs is an "incredible performer."

Olly Murs and Niall Horan using the Twitter Mirror at London's O2 Arena

Olly Murs and Niall Horan using the Twitter Mirror at London's O2 Arena

The One Direction star gushed about his close friend and fellow former 'X Factor' contestant after showing up to support him at his third gig at London's O2 Arena last night (05.05.15).

The Irish heartthrob, 21, took to Twitter to praise his pal's energetic performance, writing: "Went to watch one of my best friends at the O2 tonight Mr. @ollyofficial, the guy is an incredible performer. super craftsman."

The duo posed for several pictures in the venue's Twitter Mirror after the concert.

The O2 is the first venue in the world to have the permanent feature installed backstage which enables celebrities to take "selfies" by simply tapping the screen.

Olly also shared another image of them hanging out backstage, with the caption: "Still at the @TheO2 after the show with @NiallOfficial raving in the Arena! #goodtimes (sic)"

The 'Heart Skips a Beat' hitmaker previously admitted Niall is his favourite member of One Direction.

The 30-year-old star said: "I'd probably say the person I've spent the most time with is Niall. We play golf together, we hang out a play FIFA...

"The [others are] all busy in different parts of the world. They've all got girlfriends and they've all got their separate things going on. Niall is just someone I've kept in contact with."