He is holidaying in the south of France, while she is in upstate New York with their two children, Dylan, 13, and Carys, ten, helped by her mother Pat.
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No one knows how long the relationship has been under strain or if they can repair what went wrong.
Her spokesman has confirmed: "Catherine and Michael are taking some time apart to evaluate and work on their marriage. There will be no further comment."
This decision will have been very hard for the actress who once said it was in "her genes" to stay married for life. She added: "I will never get divorced, never."
Certainly the news has astonished their fans. When the Welsh beauty wed a movie star with a chequered past and 25 years her senior, naysayers didn't give the marriage much chance.
Over the time they appeared to have the perfect union: loving, mutually supportive and able to withstand life's shocks.
In this special report HELLO! looks back the A-list romance that had Hollywood transfixed from day one.