Catherine Zeta Jones, Michael Douglas separate

Michael Douglas and Catherine Zeta-Jones' 13-year-old marriage has reportedly hit a rough patch.

The Hollywood star couple have separated to 'evaluate and work on their marriage', according to a statement via their publicist that was released after reports their marriage had hit the rocks, reported Los Angeles Times.

'Catherine and Michael are taking some time apart to evaluate and work on their marriage. There will be no further comment,' a representative said.

This decision was apparently made after Douglas returned from the Cannes Film Festival in May.

The couple married in 2000 and have two children together, Dylan and Carys. There is a 26 years age difference between the two actors although this does not appear to have been a factor in their decision to separate.

According to a source close to the couple, Douglas' battle with throat cancer and Zeta Jones' treatment for bipolar disorder have created difficulties within the couple's relationship.

This separation may only be a temporary arrangement as neither party have sought divorce or any other form of legal action.

Other sources have said there is a chance the couple will reconcile. The couple appear to have been taking some time apart more recently as Douglas is holidaying in Sardinia alone, whilst Zeta-Jones is with their two children in New York.

When at home in the US, the couple live in separate houses -- Douglas in Manhattan and Zeta Jones in their upstate New York property.

Further back, both actors have been busy of their own projects. Zeta-Jones recently appeared in Red 2 while Douglas starred in Liberace biopic Behind the Candelabra.