United Kingdom, Feb. 11 -- Ansel Elgort finds fatherhood "exhilarating".

The 31-year-old actor was revealed to have quietly become a dad for the first time last month when he was pictured with his child in a baby carrier alongside a mystery woman, and he has now shared a photo of himself with his son.

He captioned the Instagram post: "Fatherhood is exhilarating, exhausting, it's everything and more. The present feels more present and the future brighter.

"He wakes us up all night and yet I've never felt stronger during the day. He goes from crying to laughing, expressing everything he feels and it's freed me to do the same.

"I wanted to keep it sacred, just for us, but now I want to share this story with you as it's the brightest happ...