The 30-year-old actress, who has not confirmed her pregnancy, looked the picture of happiness as she danced in the arms of her future husband. The couple were enjoying a weekend at the Stagecoach Country Music festival in Indio, California.
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Wearing a pink and purple chequered shirt and baggy jeans, Mila dressed down for the first day of the event. The Ukraine-born beauty hid behind her shades and cuddled up to Ashton as they bopped along to the music onstage.
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Ashton, 36, fitted in with his fellow country music fans perfectly as he donned a red t-shirt, black jeans and a cowboy hat. The Two and a Half Men star wrapped his arms protectively around Mila and her blossoming bump and was pictured gazing lovingly at his fiancée.
The loved-up couple, who usually keep a low-profile, couldn't resist getting into the spirit as they broke into a dance and clapped along to the music. The pair then surprised audiences when they leapt up and joined singer Johnny Van Zant of Lynyrd Skynyrd on stage.
The trio clutched on to each other and danced around in a circle, waving an American flag, to many cheers and shouts from the crowds.
The following day, Ashton and Mila were back on top form as they enjoyed round two of the music festival. The Black Swan actress kept her baby bump under wraps in a loose-fitting orange patterned top and denim shorts, while Ashton went the whole nine yards in dungarees, a blue bandana and a black cowboy hat.
Wedding dresses Mila could wear on her big day
Ashton and Mila have been dating for around two years but first met while filming hit sitcom That 70s Show in 1998. The couple are said to have got engaged early this year but have no plans yet as to when they will walk down the aisle.
Ashton was previously married to actress Demi Moore while Mila was in an eight-year relationship with child star Macaulay Culkin, which ended in 2010.