Floyd Mayweather has a brand new baby sister -- this according to a DNA test which shows the boxer's famous father, Floyd Mayweather Sr., is the daddy to a 1-year-old girl!
65-year-old Floyd Sr. -- who famously trained his son during his legendary career -- has been in a paternity dispute with a woman named Purisa Farris, who filed for child support earlier this year.
Now we've learned, as part of the case ... Floyd took a DNA test back in April which showed the probability of paternity is 99.