Alex Rodriguez, Jennifer Lopez
Jose Canseco claims Alex Rodriguez is cheating on Jennifer Lopez. Pictured: Alex Rodriguez (L) and Jennifer Lopez attend the 2019 Vanity Fair Oscar Party hosted by Radhika Jones at Wallis Annenberg Center for the Performing Arts on February 24, 2019 in Beverly Hills, California. Getty Images/Dia Dipasupil

Jennifer Lopez and Alex Rodriguez have just gotten engaged, but cheating allegations are already marring the beginning of the next chapter in their relationship.

Former baseball star Jose Canseco recently made shocking allegations against Rodriguez, claiming that A-Rod is cheating on Lopez with the former's ex-wife, Jessica Canseco. Canseco revealed the alleged affair on his Twitter page while he was watching Lopez's NBC reality show, "World of Dance."

In his first tweet, Canseco said that he was watching Lopez send a message to Rodriguez, but she had no idea that he was "cheating on her with my ex-wife Jessica." The former baseball star added that he felt sorry for Lopez because "she has no idea who he really is."

Canseco went on to bash Rodriguez in a follow-up tweet that, imploring that he "stop cheating on Jennifer Lopez." He also claimed that he had been with his ex-wife when he witnessed Rodriguez calling her on the phone.

Standing by his allegations, Canseco said that he was willing to take a polygraph test to prove that his statements were "100 percent accurate." He also challenged A-Rod to a "boxing match or an MMA match," saying he was up for it anytime.

Neither Lopez nor Rodriguez has commented on Canseco's cheating allegations.

His claims come just a day after Rodriguez popped the big question to Lopez just weeks after they celebrated their two-year anniversary. The couple announced their engagement via Instagram over the weekend by sharing a snap of the singer-actress' diamond engagement ring, which has been estimated to cost $4.4 million.

Lopez apparently proposed to the 49-year-old singer at a beach while they were vacationing in Baker's Bay.

Benny Medina, Lopez's rep, also confirmed that she and Rodriguez have gotten engaged in a statement to People.

Meanwhile, Canseco has a history of battery and assault. He was previously arrested and charged with battery after beating ex-wife Jessica during an argument back in 1997.

He was also charged with aggravated assault after hitting first wife Esther Haddad's BMW with his Porsche. The former baseball pro received community service.