Niall Horan has asked for privacy after undergoing knee surgery that he claims was "much larger than anticipated." The One Direction singer was pictured last week walking on crutches with a large cast on his knee after arriving at Heathrow airport. Naturally, at the sight of the surprising new snaps, Horan's avid fans took to Twitter to demand to know what was what going on.

Niall Horan
Niall Horan Has Asked For Privacy After Undergoing Knee Surgery.

The 20 year-old reassured his fans and let them in on what was going on: "Hey guys I know most of you have seen those pics today! Yes I've had major knee surgery , a much larger surgery than first anticipated , But i would like to tell u , it was a complete success ! Considering the scale of it!" he tweeted. "So all I ask of you guys is that you would respect my Privacy as I try to recover and get for the where we are tour!" Niall wrote, prompting a stream of support from his followers.

Niall Horan This Is Us
The One Direction Star Revealed The Surgery Was More Serious Than Expected.

The Irish singer was spotted in the less-than-glamorous attire of a grey hoodie, trainers and football socks after reportedly having not long been back in the UK from the US. The 1D star has spoken about his unreliable knees in the past and is known to have undergone surgery in October 2012 to fix torn ligaments in his knee. It seems like he'll have until April to recover, when he'll be needed with his four bandmates to kick off their Where We Are tour in Bogota, Columbia.

One Direction
Niall Will Need To Rest Up Before 1D's Tour Kicks Off In April.

Horan, who is rumoured to be dating underwear model Barbara Palvin, has seemingly eroded his own request for privacy by sharing a number of selfies with fans since his surgery. "Thank god for filters huh! Be in an awful state without them hahaha," he captioned one photo taken in the back of a car. Directioners: it looks like Niall will be just fine.