The 30-year-old actress will appear in an upcoming episode of the US sitcom, CBS broadcast announced Tuesday.
Kunis will play Vivian, a young, free-spirited traveller, who turns up on Walden’s (Ashton) doorstep and plays with his heart strings.
Walden believes Vivian is “the one”, but her appearance causes a stir as he was just about to propose to someone else, reports contactmusic.com.
Meanwhile, Kunis and Kutcher, who starred as an on and off couple on Fox’s “That ’70s Show” from 1998 to 2006, sparked rumours they got engaged last week after the “Ted” star was spotted wearing a diamond sparkler on her ring finger while she was shopping in Los Angeles, California.
Kutcher, who was married to Demi Moore before divorcing her last year, started dating Kunis in April 2012. They have been inseparable ever since.