Moore, 49, and Kutcher, 33, were wed in September 2005, but the couple's relationship became tabloid fodder in recent months as rumors swirled about Kutcher's alleged infidelity.

``It is with great sadness and a heavy heart that I have decided to end my six-year marriage to Ashton. As a woman, a mother and a wife there are certain values and vows that I hold sacred, and it is in this spirit that I have chosen to move forward with my life. This is a trying time for me and my family, and so I would ask for the same compassion and privacy that you would give to anyone going through a similar situation,'' she said in her statement to the AP.

The pair frequently used Twitter to communicate with each other as millions of fans followed along.

``I will forever cherish the time I spent with Demi,'' Kutcher tweeted Thursday. ``Marriage is one of the most difficult things in the world and unfortunately sometimes they fail.''

Moore said in 2007 that her May-December relationship with the star of ``That `70s Show'' and ``Punk'd'' _ who is 15 years younger than Moore _ ``caught us both by surprise.''

``If somebody would have said, `OK, here is the prediction: You're going to meet a man 25 years old and he's going to see being with you and having your three kids as a bonus,' I would have said, `Keep dreaming,''' Moore said in a 2007 interview with Vanity Fair. ``I think it caught us both by surprise, and particularly him.''

Kutcher became a stepfather to Moore's three daughters _ Rumer, Scout and Tallulah Belle _ from her 13-year marriage to actor Bruce Willis. Moore and Willis divorced in 2000 but remained friendly. Moore and Kutcher were photographed socializing with Willis, and the couple attended Willis' wedding to model-actress Emma Heming in 2009.

Moore and Kutcher created the DNA Foundation, also known as the Demi and Ashton Foundation, in 2010 to combat the organized sexual exploitation of girls around the globe. They later lent their support to the United Nations' efforts to fight human trafficking, a scourge the international organization estimates affects about 2.5 million people worldwide.

Moore can be seen on screen in the recent films ``Margin Call'' and ``Another Happy Day.'' Kutcher replaced Charlie Sheen on TV's ``Two and a Half Men'' as is part of the ensemble film ``New Year's Eve,'' set for release next month.