Claressa Shields has dropped a huge bombshell after revealing she took part in a secret sparring session with long-running boxing rival Savannah Marshall.The two-time Olympic champion has ramped up the feud between the two fighters by claiming she "pulverised" the Brit in the build up to Rio 2016.The pair are both signed to Sky Sports Boxing and BOXXER, with a highly sought after grudge match on the cards.Shields boasts an extremely impressive fighting CV – a 100 percent professional win record, back-to-back Olympic gold medals, and two World Championship titles. She also recently made her mixed martial arts debut – winning her first ever fight via technical knockout. Her rivalry with Marshall started all the way back in 2012, when she was beaten by the Brit in an amateur bout. This is the only fight T-Rex has ever lost in her entire boxing career.Looking for revenge, Shields faced Marshall in a secret sparring session four years later, she has now revealed all about the clandestine bout."I whooped her ass," the US native told Sky Sports. "I made her face as orange as my hair!"The sparring session was simple. I had my hands down the entire time. She could not land a punch on me."Shields then bragged she 'pulverised Marshall for four rounds' after refusing to switch roles during the session.However, Marshall laughed at Shields' recollection of the meeting and teased: "When has Claressa ever battered anyone? There is your answer."The former Commonwealth champion has completely shut down Shields' claims. In fact, Marshall stated her opponent only managed to "throw about 10 shots" the entire session during the Team GB and Team USA training camp."Can you batter someone with just 10 shots? I'm surprised she hasn't said that I was on the canvas!"The two women have been goading each other mercilessly this year and revving up the hype surrounding a mouth-watering clash. ENTER GIVEAWAYShields is a very outspoken fighter and doesn't shy away from making bold claims. She recently refused to fight on the undercard of a Jake Paul vs Tyrone Woodley headliner, stating: "I would never fight on the undercard of someone who does not possess the skills or accomplishments that I have."She then went as far as saying she "could beat up Jake Paul" as she demanded her name and status be respected.

In the summer, Shields took to Twitter to offer Marshall a bout this December. If it does take place, it will now be the mother of all boxing matches after T-Rex's sparring bombshell.

It's been a long-standing nine years of rivalry between the two, which could all boil down to a thrilling winter meeting.

"The fight will happen and we'll see who has been lying for this entire time," Shields said.