Mel B says she had sex with fellow Spice Girl Geri Halliwell

In a tell-all interview for Piers Morgan's Life Stories, Melanie Brown aka Mel B, 43, dropped a bombshell revealing that she had sex with a fellow Spice Girl.

Brown, aka Scary Spice -- who identifies as bisexual -- shocked the veteran TV journalist when she let slip that she once hooked up with Geri Halliwell aka Ginger Spice, 46.

Shocking Melanie C aka Sporty Spice -- who was in the audience during filming --Brown's revelation (which it turns out she left out of her forthcoming biography Brutally Honest), comes as the Spice Girls are about to embark on their first world tour in over 10 years.

"We were best friends. It just happened. Have you ever done that?" She asked Morgan, 53.

RELATED: Spice Girls reveal we've been singing this iconic lyric wrong

When pressed, Brown said, "[Halliwell] 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 added, "[Halliwell] had great boobs."

When Morgan asked her if it was "just once?" Brown said, "yeah."

Suddenly realising that Brown's announcement was previously not public knowledge, Morgan called it, "A Spice Girls bombshell."

"This is a bombshell. A Spice Girls bombshell. You have never admitted this before have you? People are going to be fascinated."

Brown -- while no doubt coming to terms with the fact that possibly said too much -- replied, "Yeah and I have said it now. All done. 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."

The Sun reported that according to friends, Halliwell's hubby -- F1 motor mogul Christian Horner -- is unlikely to be particularly jazzed about Brown's latest bedroom confession.

Sources also told the publication that Brown allegedly made a panicked phone call to Halliwell in an effort to do some serious damage control.

"The girls all know Mel struggles to keep her mouth shut but Mel C who was in the audience was visibly horrified when it all came out.

"The tour is just two months away they don't want anything jeopardising it, but there were real fears this would upset Geri's husband and cause serious issues."

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

While Brown withheld sharing details of their alleged romp, The Sun reported that the one-night stand happened some time in the mid '90s after the band moved into a shared house.

Brown also admitted to kissing Melanie C, 45, to try out a new tongue piercing.

"It was just a silly kiss. Nothing sexual like that," she told Morgan.

RELATED: The 'real' reason Victoria Beckham isn't joining the Spice Girls for their reunion tour

The tour -- which kicks off in June in Manchester -- was announced last November and does not include Victoria Beckham aka Posh Spice.

"Speaking candidly on The Jonathan Ross Show, Mel C said, "I saw Victoria recently and obviously, we've all been in contact. She is still very much a part of the Spice Girls, she really supports us and we really support her."

She added, "But she did raise the point that she was never actually asked. We just presumed."