Girls Aloud have unveiled a teaser trailer for their comeback single.

The 'Biology' hitmakers - who announced last week they will be making a major announcement on Friday (19.10.12) - are seen in the clip walking away from the camera in slow motion.

Just as they are about to turn in unison, the video cuts to black and flags the announcement, which will be made live on YouTube on Friday.

All five members, Cheryl Cole, Nicola Roberts, Nadine Coyle, Sarah Harding and Kimberly Walsh, are dressed in identical orange dresses with their hair up in buns.

What appears to be the group's comeback single plays in the background throughout.

The reunion - which comes after the quintet went on indefinite hiatus in 2009 - coincides with the group's 10th anniversary and is expected to consist of a new single, 'Greatest Hits' compilation and a UK tour.

However, fans who are hoping the reunion is permanent could be in for a nasty surprise as Cheryl hinted in her new autobiography that they will call it a day after their tour.

She wrote: ''We'll be working on a tour and greatest hits album. Then I think that's it for Girls Aloud.

''We've achieved more than any of us ever dared to dream of.''