The long-rumored, much-anticipated but never-quite-done fight between Conor McGregor and Floyd Mayweather might be a little closer to reality.

McGregor, the biggest star in mixed martial arts, signed a contract with the UFC last week for his side of the cross-sports boxing match.

With his end of the deal signed, the brash 28-year-old McGregor, who is 21-3 in UFC, posted a message to Mayweather on his Twitter account Sunday encouraging the former pound-for-pound to sign his side of the contract.

"Sign your end Floyd or you are just a mouth," McGregor stated.

Mayweather, 40, has not fought since September 12, 2015 when he won a twelve round decsion over Andre Berto. He is 49-0 and has won world titles at five different weight classes. He added to the speculation with comments over the weekend while in London for a fight involving his protege Gervonta Davis.

“I think the fight will happen,” Mayweather said in the ring after Davis defeated Liam Walsh. “I had a great career and my career may not be over. No. 50 might be against Conor McGregor. We’ll just have to wait and see.”

In a pre-fight interview, Mayweather said he needed to communicate with his team back in the United States.

“The only fight that makes sense to me is the McGregor fight. I’ve accomplished everything I want to accomplish, but I guess I have one more obstacle to get over,” Mayweather said.

Mayweather was clear on one thing, however. If the fight happens, he expects to be paid more than McGregor.

“We do know I’m going to be the ‘A’ side,” he said, noting that he has made $800 million in his career. “... It wouldn’t hurt to throw a couple hundred million on top of that.”

Mayweather made $44 million in 2016, according to Forbes, which reported that Mayweather’s fight against Manny Pacquiao set several records, including most pay-per-view buys (4.6 million) and total gate ($73 million).

In April, McGregor said he expected to make more than $100 million in a fight against Mayweather. McGregor made $22 million in 2016, according to Forbes.