Robbie, a judge on the current series of The X Factor, may get on stage with his former bandmates once more.
The Sun reports that the group are planning the guest appearance to celebrate their 30 year anniversary, ahead of a new tour in 2019.
An insider said: “It seems a shame to have one of the biggest pop stars on the planet sat there and not hear him, so they’ve been plotting a surprise for the end of the series.
“It’s a while since they got together and nobody is completely sure when it was going to happen for the anniversary so it’ll be a massive moment.”
It was claimed on ITV's Lorraine on Friday that Robbie will indeed join the group on stage, but there's been no official confirmation yet.
Meanwhile, Robbie will be returning to The X Factor on Saturday night after three weeks away. Nile Rodgers sat in for him as Robbie performed at pre-arranged tour gigs in South America.
This weekend is a an ABBA themed special with the remaining contestants singing hit songs from the Mamma Mia soundtrack. ABBA legends Benny Andersson and Björn Ulvaeus are joining with The X Factor to for the weekend. Plus, there will be a guest performance from some of the cast of the Mamma Mia movie.
Two acts left the show on Sunday leaving a total of six contestants currently on the show.
Left in Louis Tomlinson's Boys are Anthony Russell, Brendan Murray and Dalton Andre Harris. Ayda Williams' Overs are down to just Danny Tetley.
Simon Cowell's Girls left with only Scarlett Lee. Finally, the Groups mentored by Robbie are now just duo Acacia and Aaliyah.
The X Factor 2018 is back on Saturday at 8PM on ITV and continues with semi-final results show on Sunday at 8PM.