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, Khazar Momeni, who was married to someone else.