How do you design a wedding dress for a princess?

Prince William and girlfriend Kate Middleton have been sent congratulations from around the world after announcing their engagement.

On Tuesday, the couple, both 28, revealed they would marry next spring or summer after the prince proposed while on holiday in Kenya in October.

Elizabeth Emanuel, who designed Princess Diana's wedding dress, spoke to the BBC about the process Kate Middleton will go through to acquire the perfect dress for her big day.