HARRY
And anyway – it has to be me.

Everyone turns to HARRY.

DRACO
What?

HARRY
For this plan to work she has to believe it’s him, without hesitation. She’ll use Parseltongue – and I knew there was a reason why I still have that ability. But more than that, I – know what it is to feel – like him. I know what it is to be him. It has to be me.

RON
Rubbish. Beautifully put, but beautiful rubbish. No way are you going to—

HERMIONE
I’m afraid you’re right, my old friend.

Harry Potter and the Cursed Child - Chapter 4 :
See this quote in the Pensive -