IT consultant Nima Momeni fatally stabbed CashApp founder Bob Lee through the heart after the pair fought about the suspect’s sister — and whether they were doing “anything inappropriate,” new court documents released Friday allege.

Police claim that before Lee was murdered on the streets of San Francisco in the early hours of April 4, Momeni and the slain tech entrepreneur had talked on the phone about his sister, who was married to someone else.

A unnamed witness told police that Momeni grilled Lee about his sister, asking if she was “doing drugs or anything inappropriate.”

Lee, 43, assured his alleged murder that nothing out of bounds had happened.

Police didn’t elaborate on the relationship Lee had with Momeni’s sister.

That night, Momeni drove Lee to a “dark and secluded area” of San Francisco, the charging documents allege, where he stabbed him through the heart with a kitchen knife.

Momeni brought the knife with him from his home, which police said makes clear the murder was “planned and deliberate.”

Momeni’s sister texted Lee around the time of his murder to check in on him, the documents claim.

“Just wanted to make sure your doing ok Cause I know nima came wayyyyyy down hard on you,” she wrote. And thank you for being such a class man handling it with class. Love you Selfish pricks,” she added.