The veteran actor plays Sirius Black in the latest movie 'Harry Potter and the Order of the Phoenix', and Daniel admits the pair enjoyed some revealing chats on set.
The 18-year-old star revealed: "Gary did give me a few really good pieces of advice about girls that I'm definitely going to stick to.
"One of them was that you've got to find out if they get on with their parents, which is a good rule of thumb.
"I can't repeat the rest. It was a private moment between myself and Gary!"
Gary recently revealed the pair formed a close friendship during filming.
He said: "The kids in the movies are excellent, and in some ways it's the closest thing to theatre, because there's that sense of the company.
"And you become close and don't all drift away like you do after most films. The people working on it are so good, and Dan in particular has become a good friend. We've become quite close."
WTF/LOL/EW/awww all at the same time.