(Cover) - EN Showbiz - Ashton Kutcher says you have to work at a relationship when things are going well.

The actor has been married to Hollywood star Demi Moore since 2005 and he admits it does require some effort to maintain their happiness. Ashton has learned not to take it for granted when the couple are going through a good patch and finds this to best time to evaluate their relationship and try to understand what is working.

A good relationship will ground you. I think the key to any relationship is work on it when its good, he said in an interview with British television show Lorraine. When things are going good a lot of the times people just rest. But we all have this assumption that at some point in our lives we will just be happy and we wont have to work on it anymore. And the minute you stop working on it is the minute things start to fall off. And I think in relationships and family, when its really going good work on it then and it will stay good.

The 33-year-old hunk sparked surprise when he began dating Demi, who is 15 years older than him. Despite the initial scepticism, the couple went on to get married and are still going strong. Demi has three grown-up daughters with her ex-husband Bruce Willis and Ashton has developed a close bond with them. He loves being a step-father, joking that meeting Demi was like walking into a readymade family unit.

Yes its like an instant family, a family in a cup just add water! he laughed. (C) Cover Media