The pop nostalgia show, which has reunited '90s and early '00s pop acts such as B*Witched, 911 and 5ive, has expanded its lineup to include the four-piece.
Blue - who are made up of Simon Webbe, Lee Ryan, Duncan Jones and Anthony Costa - formed in 2000 and scored hits with tracks such as 'All Rise', 'Too Close' and 'If You Come Back'.
They originally split in 2005, but reunited in 2009 and have been working together on-and-off since then. They famously represented the UK in Eurovision in 2011 with the track 'I Can', finishing 11th.
Technically the group are not 'reuniting' for the show as they released a new album - Roulette - in several European countries earlier this year. The group are expected to release the record in the UK later this year.
The Big Reunion airs on Thursday nights at 9pm on ITV2.
Watch our video with the stars of The Big Reunion below: