The first major trade in MMA history is a done deal.

UFC has officially agreed to release former flyweight champion Demetrious Johnson from his contract in order to allow him to sign with ONE Championship.

In return, ONE has agreed to release former welterweight champion Ben Askren from his contract in order to sign with UFC.

Considering both fighters had multiple fights left on their respective contracts, a transaction of this magnitude has never been done before in MMA.

One Championship CEO Chatri Sityodtong officially announced the transaction on Twitter on Saturday, while Johnson expressed his excitement with the move on a social media post.

Both Johnson and Askren are expected to sign deals with their new organizations in the near future, sources told ESPN.

After Johnson (27-3-1) lost the title to Henry Cejudo in August, sources told ESPN that a plan was hatched to leave UFC. However, UFC needed incentive to release Johnson from his deal. Sources said that's when Johnson's representatives at First Round Management came up with the idea to pitch sending Askren over to UFC, pending his consent.

Matt Hume, Johnson's coach at AMC Pankration in Kirkland, Washington, also serves as ONE's vice president of operations.

Once all parties agreed on the parameters of the transaction, the deal was finalized.

The loss to Cejudo snapped Johnson's 13-fight win streak as well as his record streak of 11 successful title defenses.

Askren (18-0, 1 NC), a former Bellator welterweight champion, announced his retirement following his first-round victory over Shinya Aoki in November 2017. Following his announcement, however, Askren said he was open to fighting the likes of Georges St-Pierre or Rory MacDonald.

Askren and Johnson, amid recent trade reports, have acknowledged the transaction on social media. Askren has gone a step further by picking fights with some of the biggest names on the UFC roster.

Debuts for both fighters have not been set at this time.