She bowed out from the UK X Factor after the 2010 series to take up a short-lived place on the panel for the US version of the show.
Cole ruled out a return as a judge, but agreed to a temporary comeback helping out Barlow as he took his hopefuls to a country pile in Northamptonshire.
The erstwhile Girls Aloud singer - who was given her big break on TV talent show Popstars: The Rivals - tells the contestants she can sympathise because she has been in their position.
Cole says: “I’ve been there and I have been here so I know how you are all feeling, I am just excited to see what you have got.
“Think it’s going to be amazing and I wish you the best of luck from the bottom of my heart.”
Viewers will see the contestants finding out which judge will lead each category and for some acts it is a bit of a shock to the system.
Nicola Marie Bloor from Derby thinks she is on a sticky wicket when she finds herself in Barlow’s group.
“I felt sick when I saw Gary as he obviously finds me very irritating, I was worried straight away,” she says.
Other guest mentors include Tinie Tempah, who teams up with Tulisa Contostavlos, Ne-Yo who accompanies Nicole Scherzinger and Sharon Osbourne who is the sidekick to Louis Walsh. They will sit through performances by their contestants in tonight’s edition.
Viewers will tomorrow find out who has made it through to the live shows when the judges reveal who they have chosen to take through.
They each choose three of their six acts, but X Factor fans will have a chance to vote for a wildcard act to put through to the live section of the show.