Mila Kunis and Ashton Kutcher

Mila Kunis and Ashton Kutcher

Mila Kunis is to guest star on 'Two and a Half Men'.

The 30-year-old actress will appear opposite her fiancé Ashton Kutcher, 36, in an upcoming episode of the US sitcom, CBS announced on Tuesday (04.02.14).

The brunette beauty 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.

Meanwhile, Mila and Ashton - who starred as an on/off couple on Fox's 'That '70s Show' from 1998 to 2006 - sparked rumours they had got engaged last week after the 'Ted' star was spotted wearing a diamond sparkler on her ring finger while out shopping in Los Angeles, California.

The funnyman - who was married to Demi Moore before divorcing her last year - started dating Mila in April 2012 and they have been inseparable ever since.

However, Mila has previously claimed she isn't interested in tying the knot, but hasn't ruled it out in the future.

She said: "I would love to find 'The One'. But I'm not sure about marriage. I see no need. I'll be with somebody because I want to, not because a piece of paper tells me I have to. That said, if the love of my life thinks it's important, then fine, I'll get married."