By Mike Coppinger

Everyone was waiting for the official word on an expected Floyd Mayweather vs. Robert Guerrero fight, but the pound-for-pound king threw everyone a curveball late Tuesday night.

"Money" Mayweather (43-0, 26KOs) announced on Twitter and Facebook that he's close to fighting Devon Alexander (24-1, 13KOs). The fight would take place May 4 at the MGM in Las Vegas. Both Mayweather and Alexander are represented by powerful boxing adviser Al Haymon.

"The negotiations for my fight are almost done," said Mayweather via the social media portals. "The front runner is IBF Champion Devon Alexander. It'd be a unification bout at welterweight."

This announcement comes just days after Alexander pulled out of a Feb. 23 Showtime fight with Kell Brook. Alexander cited a biceps injury and said he would be ready in six weeks time. The bout with Brook was originally slated for Jan. 19, but Brook was forced to pull out with injury.

It's unclear at this time what occurred in the negotiations with Guerrero, but it was thought by most in the boxing world that it was a mere formality that "Mayweather-Guerrero" would be on the Vegas marquee come Cinco de Mayo weekend.

Mayweather's last fight came in May 2012, a unanimous decision win in perhaps his most exciting fight ever. Alexander defeated Randall Bailey in Oct. in a grossly boring bout.

Follow Mike Coppinger on Twitter: @MikeCoppinger