The pair clambered into an old-fashioned metal bathtub together to shoot a scene for the new U.K. TV mini-series, in which they play young and older versions of the same doctor, Vladimir Bomgard.
Radcliffe had been looking forward to shooting the scene with Hamm, but admits filming turned into a nightmare as they sat there topless in freezing cold water.
He tells British newspaper The Sun, ""I am the envy of every woman ever (after bathing with Hamm)! At the time I thought, 'Oh, I like baths, that will be a fun scene' - then the water went cold and we were sitting there shivering, and then the hot water failed and the crew had to fill it up with water from the tea and coffee stand!""
However, the Harry Potter actor is full of praise for Hamm, adding, ""Jon is really funny, personable and lovely. He's also one of the best actors I've ever seen. He even choreographed a fight scene between my character and his when the stunt co-ordinator hadn't been brought on set and we were on a tight deadline.""