"The first, and most important part of this historic contract has now officially been signed off on," said McGregor said in a statement to Themaclife.com.

The latest development marks a significant step forward in making the fantasy showdown between these two combat sports superstars a reality.

Despite that, there’s no telling how would the negotiations with Mayweather could bring as White now moves from working with McGregor and beginning talks with Mayweather’s camp.

UFCE president Dana White told TNT, McGregor had agreed to the bout.

"The McGregor side is done," White said while appearing as a guest on the network's postgame wrap-up of Game 1 of the Eastern Conference finals. "I'm starting to work on the Mayweather side now.

"I'm not saying the fight will happen, but I've got one side done, now it's time to work on the other. If we can come to a deal with Haymon and Mayweather, the fight's gonna happen."

White added the much-anticipated bout would be "straight-up boxing."