The actor met Rosanne Coker, a fellow Brit, while shooting Harry Potter and the Half-Blood Prince in 2007, and they continued to work together on the final two boy wizard movies, The Deathly Hallows Part 1 and Part 2.
But they waited until shooting had wrapped before they began their romance, according to Coker's father Malcolm.
He tells Britain's Daily Mirror, "They are a really nice couple but only got together after the latest Harry Potter film had finished filming because they thought it might cause problems.
"They worried it might be unprofessional because he was playing the main character in the Harry Potter film and they both decided it was best to wait."
Last month (Jul11), Radcliffe revealed he had been secretly dating, but refused to name Coker as the woman he was "very much in love with".
Last month (Jul11), the British actor revealed he had been secretly dating, but refused to name the woman he was "very much in love with".
However, Radcliffe has since been snapped holding hands with his mystery partner in New York, where he's currently starring in Broadway musical How to Succeed in Business Without Really Trying, and she's been identified as production assistant Rosanne Coker.
Radcliffe first met the 22-year-old brunette, a fellow Brit, while shooting Harry Potter and the Half-Blood Prince in 2007, and they continued to work together on the final two boy wizard movies, The Deathly Hallows Part 1 and Part 2.
Coker's dad, Malcolm, has confirmed his daughter is dating Radcliffe, but insists their relationship only turned romantic last year (10).
And he's given the actor the thumbs up.
Malcolm Coker tells Britain's Daily Mail newspaper, "I don't want to say too much really as they would really prefer to keep things quiet. But Rosanne has worked on the last three Harry Potter films, so she and Daniel have known each other quite a long time. They have been going out for just over a year now.
"I have met Daniel and he is a lovely guy. I'm just really happy for Rosanne and as long as she is happy that is all that matters to me. No other parent would ask any more. I know it's not a normal life they live. But they have a lot of fun together and, at their age, what more could you ask? Who knows where it is going to lead?"