Alex Rodriguez has been accused of cheating on his new fiancee Jennifer Lopez by former baseball star Jose Canseco.

The retired sportsman revealed on Saturday (09Mar19) that the Jenny from the Block singer had accepted his proposal after two years of dating during a vacation in the Bahamas.

While the couple were still basking in their happy news on Sunday, fellow retired baseball star Canseco hit them with claims that Alex has been cheating on the World of Dance judge with his ex-wife Jessica, who he divorced in 1999, in a series of bombshell tweets.

"Watching World of Dance watching J.Lo text Alex Rodriguez little does she know that he is cheating on her with my ex-wife Jessica. Poor girl, she has no idea who he really is," Canseco tweeted. "Alex Rodriguez stop being a piece of s**t stop cheating on Jennifer Lopez."

He also seemingly referred to Rodriguez and Jessica when he continued, "I was there a few months back with her when he called her on her phone."

Canseco then provided Jennifer with his phone number and asked her to call "if you want the truth about Alex Rodriguez" and said he was willing "to take a polygraph to prove that what I'm saying about Alex Rodriguez is 100 per cent accurate."

He also bizarrely challenged Alex to a boxing or mixed martial arts (MMA) match.

This isn't the first time Canseco has accused his fellow former New York Yankee of having an affair with his ex and the mother of his 22-year-daughter Josie.

Their long-running feud dates back to 2008, when Canseco first made the infidelity claims. In his 2008 book Vindicated he alleged that Alex had bombarded Jessica with messages and phone calls and he told reporters he was "pretty sure" they hooked up.

The couple are yet to respond to his tweets.