Daniel Radcliffe was Emma Watson's 'love guru' on sets of Harry Potter

Emma Watson and Daniel Radcliffe became romantic coaches for each other on the sets of Harry Potter.

The star-studded cast, who is reuniting for a special episode on HBO Max nest year, revealed that fourth franchise in the film titles Goblet of Fire, was all about crushes and 'flying' hormones.

"The Goblet of Fire is all about teenagers having crushes for the first time. They really mirrored all those kind off awkward phases you go through as a teenager and they really felt like that too because we were literally having the same experiences." Rupert Grint began in the interview. "It was an interesting film in terms of a lot of hormones flying around."

Daniel Radcliffe added Emma Watson played romantic coach to him on multiple occasions and viceversa.

"The amount of prep and coaching Emma and I would have to give each other on, like, texting to the opposite sex if I was texting a girl or if she was texting a boy. I'd go, 'She sent me these many kisses back. What do I do? It's a nightmare'."

"We had that kind of older brother, younger sister thing," added Emma of their sibling-like bond.

Harry Potter 20th anniversary reunion - Return to Hogwarts will premiere on HBO Max January 1.