Four months after losing the US presidential election to Barack Obama, Mitt Romney is joining his son's investment firm, a Romney adviser said last night.

Last year's Republican presidential nominee will serve as chairman of the executive committee at Solamere Capital, an adviser said, who asked not to be identified.

A formal announcement is expected later this week. The move was first reported by NBC News.

Mr Romney's son, Tagg Romney, co-founded Solamere in 2008 with Eric Scheuermann and Spencer Zwick, Mitt Romney's finance chairman in his 2008 and 2012 presidential campaigns.

Mitt Romney co-founded the private equity firm Bain Capital before serving as Massachusetts governor.