A PHOTO of a One Direction singer posing with fans has gone viral as people noticed a former Celtic star in the background. 

Former boyband member Louis Tomlinson was spotted arriving at Melbourne Airport to perform three Australian dates as part of his world tour. 

A fan shared a photo of the 30-year-old posing with a group of delighted fans in the airport - but football fans have noticed something else in the picture.

In the background walking past the group is none other than former Celtic player Tom Rogic. 

Twitter went wild at the unexpected photobomb by the Australian midfielder, who departed the Hoops at the end of last season and was known affectionately by Celtic fans as The Wizard of Oz.

One person shared a zoomed-in image of Rogic and wrote: "This is the real superstar." 

Another joked: "Such a talented man, and Louis."

One wrote: "The Wizard of OZ!"

While another Twitter user shared a photo of both Rogic and Louis playing in Celtic colours, as the What Makes You Beautiful singer previously donned the Hoops for a charity match. 

They wrote: "Imagine randomly catching two guys that have worn these hoops at Celtic Park in one photo!"