The 33-year-old actor starred with Helen, 65, in `Phedre` two years ago and although Dominic - who has previously dated `Mamma Mia` co-star Amanda Seyfried - attempted to woo Helen, he admitted she failed to succumb to his charms.
He told Live magazine: "Helen`s incredibly hot. I tried so hard to make her fancy me, but I just knew immediately that there was nothing. She didn`t fancy me at all."
Getting close to his gorgeous female co-stars is one of the best things about Dominic`s job and he revealed spending the day in bed with Keira Knightley on the set of `The Duchess` was a "really nice" experience.
He said: "It`s not been bad. People always complain about love scenes saying it`s awkward with so many people around. The fact is that it`s lovely lying in bed with a beautiful woman. Being with a naked Keira Knightley is a really nice way to spend the day."
However, Dominic is wary of getting typecast as a love interest, explaining: "It`s a very easy category to fall into. Some people I`m sure love doing that, but it`s kind of mind-numbing. Beyond the vanity of watching yourself be the love interest in a reasonably good film, it doesn`t interest me."