The girl group is set to hit the road in May. 

Mel B, aka Melanie Brown, made a major revelation this week that may have put The Spice Girls' long-awaited reunion tour on hold.

While filming a new episode of Piers Morgan's Life Stories, Scary Spice admitted that she once had a casual fling with her bandmate Geri Halliwell. "We were best friends. It just happened," Mel told Morgan, according to The Daily Mail.

After dropping the major bombshell, it appeared as if the singer instantly regretted her words, saying: "She is going to hate me for this because she is all posh in her country house and her husband, but it's a fact. It just happened and we just giggled at it and that was it. She had great boobs."

Spice Girls
Credit: Photoshot/Getty Images

Brown continued: "She is going to kill me and so is her husband. Hopefully when Geri gets asked that, which hopefully she will after this, she won't deny it, because it was just a thing, a fun thing."

Meanwhile, fellow Spice Girl Mel C was in the audience during the taping and seemed completely shocked by the news, which caused Brown to give Geri a call, according to The Sun. "The tour is just two months away they don't want anything jeopardizing it, but there were real fears this would upset Geri's husband and cause serious issues," a source said.

Geri married race car driver Christian Horner in 2015 and the couple share a son: 2-year-old Montague.

"Since marrying Christian, Geri has worked hard to shake off her old playgirl image and sort of reinvent herself as this perfect Stepford Wife," the insider went on. "Mel immediately rang Geri to try to repair the damage."

The Spice Girls' 13-date tour kicks off on May 24 in Dublin, Ireland, and will end in the band's native London on June 15. If they keep their original schedule, there could be some awkward on-stage moments between the two BFFs — depending on how Geri takes the news.