Prongs; Time Travel Pun

The Patronus turned. It was cantering back towards harry across the still surface of the water. It wasn't a horse. It wasn't a unicorn, either. It was a stag. It was shining brightly as the moon above... it was coming back to him...
It stopped on the bank. Its hooves made no mark on the soft ground as it stared at Harry with its large, silver eyes. Slowly, it bowed its antlered head. And Harry realised...
'Prongs,' he whispered.
.
.
.
'Harry, I can't believe it - you conjured up a Patronus that drove away all those Dementors! That's very, very advanced magic...'
'I knew I could do it this time,' said Harry, 'because I'd already done it... Does that make sense?'

HERMIONE'S SECRET - Pg 438