It’s on … Floyd Mayweather is officially set to square off with Andre Berto in September … TMZ Sports has confirmed.

The two have been in talks for weeks … but now we’re told from both camps that it’s a done deal and the two will fight in Vegas on September 12th.

We spoke with Berto who tells us, “It’s a pleasure and honor to be in this position and I’m looking forward to capitalizing on every moment of it”.

As we previously reported, there’s some bad blood between the two — with Berto claiming Mayweather had been crank calling his phone … and he believes it was all over a woman.

Mayweather is 48-0. Berto is 33-3.

Story developing …