The trial heard how the group of friends had attended their school prom at the Holiday Inn.
They returned to Mr Migdal’s car – parked on Sharp-Meade’s street – where they intended to change before heading to an after-party in Cambridge.
Prosecutor Jane Bickerstaff KC told the court: “They were approached by the defendant who was armed with a large zombie-style knife. He had it concealed down his tracksuit trousers.”
She said the friends had backed away but Mr Migdal had not finished changing and “momentarily stood his ground”.
The defendant approached and stabbed him in the chest, the jury heard.
He was rushed to Stevenage’s Lister hospital, where he died in the early hours of the morning.
When the murder verdict was delivered, Mr Migdal’s family and friends, who were seated in the public gallery, gasped before crying and hugging.
Sharp-Meade will be sentenced on 17 May.
