That could all be about the change, however. The former couple put on a surprising display of solidarity on Monday when they were pictured arriving back from a conference together.
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Demi, 50, and 35-year-old Ashton — who are still thrashing out a divorce settlement — walked through the arrivals area at Burbank airport in LA, and seemed to be locked in intense but friendly conversation.
Ashton, who is now dating Mila Kunis, could be heard telling Demi about what sounded like a new project, saying, "It could really work", as they were approached by photographers eager to capture the reunion.
They eventually ended the conversation and went their separate ways, but it seems clear that the pair are on cordial terms.
They had both been attending the same tech conference in San Jose, related to their organisation Thorn, which defends children against online predators.
According to the organisation's website, the group continues the work started by the Demi and Ashton (DNA) Foundation in 2009.
Ashton and Demi were separated in 2011 after six years of marriage. The actor filed for divorce in December 2012, citing irreconcilable differences.
Since then Demi has sought spousal support from the Two and a Half Men star.
While the couple are still legally married, Ashton is in a serious relationship with That 70s Show costar Mila, who was at the Toronto Film Festival on Monday night for the premiere of Third Person.