The couple split up more than a year ago, but it is only now that the Two And A Half Men star has filed papers at the Los Angeles Superior Court stating that "irreconcilable differences" were responsible for their break-up.
Demi had previously expressed that she intended to file for divorce, but had not done so.
US gossip site TMZ, which broke the news, claims that 34-year-old Ashton had waited so long to file because he wanted to give Demi, 50, the opportunity to do it first.
In a suggestion that the couple had no pre-nuptial agreement, the papers indicate that property rights will be worked out later.
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