Her grandmother favours diamonds and pearls for official portraits. Zara Phillips, however, went for something different.

And her choice of a tight black jumper and trousers and incredibly vampish heels went down well with popular artist Jack Vettriano.

“She looked exceptionally sexy,” the Scottish painter said yesterday, adding jokingly: “Is it treason to say that?”

The Queen’s 26-year-old granddaughter – who won gold at the world eventing championships and is training with her horse, Toytown, for the Beijing Olympics – agreed to pose for her first official portrait on behalf of Sport Relief.

Vettriano, whose paintings sell for more than £700,000, was equally keen to paint the 12th in line to the throne to raise funds for the charity’s appeal.

“I don’t really do portraits so I told them I would only do it if Zara Phillips agreed,” he said. “To be honest, I never thought she would say yes. I love the way she is lying with the Union Jack draped beneath her. I think it is a very sexy and powerful image.”

The 20in by 24in oil on canvas will be auctioned later this year. (via Daily Mail)