Not even 12 hours after it was revealed that Bellator had unconditionally released lightweight champion Eddie Alvarez, the UFC has confirmed both his immediate signing and his debut. It's a fight that had been rumored for quite some time, and now it's real. Eddie Alvarez vs. Donald Cerrone is your UFC 178 co-main event.

Alvarez' first fight under the UFC banner will be a UFC 178 co-main event bout against Donald "Cowboy" Cerrone in Las Vegas on September 27. Cerrone's original opponent for that date, Bobby Green, will face an opponent to be determined on a later card.

Alvarez (25-3) has won his last 3 fights since the shock submission defeat to Michael Chandler in 2011. Knockout wins over Shinya Aoki and Patricky Freire were followed up by a much-publicized contract dispute between him and Bellator, which prevented him from joining the UFC. Once the two sides settled on a new contract, Alvarez won his lightweight title back from Michael Chandler last November in a thrilling split decision, and was scheduled to face him again on the promotion's May PPV before he pulled out with a concussion.

Cerrone (24-6, 1 NC) was originally scheduled to fight Khabib Nurmagomedov on this September 27th card, but Nurmagomedov blew out his knee minutes after the contracts were signed. Bobby Green was then pulled from his fight with Jorge Masvidal to face "Cowboy" in the co-main, which was considered disappointing to some because it seemingly put to rest the speculation of Alvarez joining the UFC. "Cowboy" is 3-0 this year, finishing Adriano Martins and Jim Miller with head kicks while dropping and choking out Edson Barboza in between those two bouts.

UFC 178 is headlined by a flyweight title fight between champion Demetrious Johnson and heavy underdog Chris Cariaso. It also features featherweights Dustin Poirier and Conor McGregor, plus Tim Kennedy and Yoel Romero.