SNAPE
Did no one teach you to knock, boy?

SCORPIUS looks up at SNAPE, slightly breathless, slightly unsure, slightly exultant.

SCORPIUS
Severus Snape. This is an honour.

SNAPE
Professor Snape will do fine. You may behave like a king at this school Malfoy, but that doesn’t make us all your subjects.

Harry Potter and the Cursed Child - Chapter 3 :
See this quote in the Pensive -