A 22-year-old man was fatally stabbed multiple times in the chest on the Upper East Side when he discovered his ex-girlfriend with another man early Tuesday, police sources said.

Xavier Olivares, 22, was knifed shortly after he spotted the woman walking hand-in-hand with the suspect near the corner of Third Avenue and East 94th Street around 1:15 a.m.

When he approached to ask what they were doing together, Olivares got into a loud argument with the suspect, identified as Gustavo Rodriguez.

The two men started fighting before Rodriguez pulled out a blade and repeatedly plunged it into the victim’s chest before running away.

The woman helped Olivares flag down a cab, which rushed him to Metropolitan Hospital where he later died.

Rodriguez was later apprehended by police. Charges against him were pending Tuesday afternoon.

The woman initially told police that she was walking down the street with the victim when Rodriguez came up and stabbed him. But she later changed her story when cops told her that her statements contradicted the account of an eyewitness who saw the attack.

The victim’s uncle said Olivares has a 1-year-old daughter named Sophia and described him as a hardworking dad.

He added that his nephew worked at a pizzeria on York Avenue and East 95th Street called Arturo’s, and was on his way home from work when he was killed.

“It doesn’t make sense,” the man’s uncle, Claudio Benito, 52, said outside the family’s Bronx home. “We don’t know what happened yet.”

The latest knife attack comes about three weeks after the NYPD unveiled a plan — dubbed Operation Cutting Edge — to stem the tide of citywide slashings, which are up about 22 percent this year.

The initiative focuses on using CompStat data to identify patterns, increasing police presence at high-slashing locations and even cracking down on the sale of box cutters.