|Catherine Zeta-Jones and Michael Douglas|
The couple - who have not been photographed together since April - have decided to separate in order to spend some time apart.
Neither Michael nor Catherine have made any movements to file for divorce or legally separate.
A source told the new issue of People magazine: "They're taking a break."
Michael, 68, is currently on vacation on a yacht off the coast of Sardinia, while Catherine, 43, is at home in New York with their two children, son Dylan, 12, and 10-year-old daughter Carys.
The two stars tied the knot in 2000 at Manhattan's Plaza Hotel but their 13-year marriage has come under intense pressure in the last three years with Michael being diagnosed with throat cancer in 2010.
The 'Behind the Candelabra' star beat the disease and has been cancer-free for two years, but Catherine was diagnosed with bipolar II disorder in 2011 and although she was treated in a mental health facility that year she had to receive more clinic-based treatment in May this year.
These two life-changing things are said to have put a massive strain of the relationship.
A friend of the couple said: "The stress has taken a toll on their marriage."
Just last month Catherine claimed she and Michael were still strong as a couple because they give each other the right amount of space.
When asked what the secret to their long-lasting marriage was, she responded: "Respect, space and a sense of humour. We spend a hell of a lot of time together, so we are careful to maintain our space.
"We recently had an extension built, to house a closet. I go in there and never come out.
"My husband knocks on the door and says, 'Can I come in?' But I've got a TV in there, and my daughter brings her friends in - they play shop, put on all my stuff. I could be in there for the whole day, happily."