Coker's father Malcolm confirmed the couple had split, reported Daily Mail.
"Rosie's not in this country at the moment. She's trying to move on. She won't want to talk about it," he said.
The painter and decorator from Woking, Surrey, had previously called Radcliffe a "lovely guy" and told how happy his daughter was.
Radcliffe is now believed to have had had a fling with Darke, an up-and-coming actress whom he met on set and wooed her with trips to London.
However, the pair are no longer thought to be together - and Darke, 28, was said to be 'devastated' when the star ended the affair recently.
Radcliffe plays Beat poet Allen Ginsberg in 'Kill Your Darlings', set for release next year, while Darke plays a character called Gwendolyn.
