Conor McGregor and Dustin Poirier shook a virtual hand on an exhibition fight in Ireland later this year.
The UFC rivals, who fought four years ago, came to an agreement to rematch for charity on December 12.
McGregor stopped Poirier in their official fight but reached out to his former rival on Twitter on Monday night.
"Hey bro! You want to do an MMA charity fight?" he wrote. "Zero to do with the UFC; I will donate half a mill towards your charity for it.
"Sell it on PPV or work a TV deal and we work out other charities that are close to my heart also. I am engaged in many. Strictly a charity 'exhibition'.
"December 12th in the Point Depot, Ireland. No weigh ins. Open weight, unified rules. I will arrange all travel fare for you and family."
Poirier, who was due to fight Tony Ferguson next month but could then not come to an agreement with the UFC over his purse, was quick to agree.
"I'm in! Let's do it! A lot of people will benefit from this," he said.
Poirier then suggested a boxing exhibition but McGregor insisted it must be mixed martial arts.
The Irishman has not fought since he stopped Donald Cerrone in January and has recently been in dispute with UFC president Dana White.
McGregor leaked direct messages between the two which showed him calling for another three fights in 2020, culminating in a rematch with Khabib Nurmagomedov.
But due to the coronavirus crisis, the UFC deemed it unviable for McGregor to fight behind closed doors due to the loss of gate receipts.
McGregor then turned his attention to Manny Pacquiao and the pair confirmed last weekend that they were close to agreeing a fight for early next year.
That remains the case but McGregor has now clouded the situation somewhat with his offer to Poirier.
