Harry learns from Professor Trelawney that her interview in the Hog’s Head with Albus Dumbledore – and subsequent prophecy was overheard by Severus Snape. Therefore it was Snape who told Lord Voldemort about the child who would defeat him (HBP25).
Harry learns that Snape was the one who told Voldemort about the prophecy
Date June, 1997
Type of Event Wizarding world