Royal bridegrooms usually have what is known as a supporter instead of a best man.
Prince Andrew had his brother Edward as his supporter and Charles had both Andrew and Edward as his supporters at his marriage to Princess Diana in 1981.
Charles, 62, ditched the tradition for his second wedding to Camilla in 2005, having no best man at all.
But his elder son is expected to choose one of his closest friends alongside Harry.
Royal insiders think that the most likely candidate is Thomas van Straubenzee, William’s oldest and closest friend. They met at Ludgrove Prep School and the charming, debonair van Straubenzee, nicknamed Van, accompanied William on his first overseas tour to New Zealand in 2005. He is one of a group of friends who have travelled with William and Kate on exotic holidays.
He was also the man William picked to accompany Kate to his Sandhurst graduation ceremony in 2006.
Other candidates are Harry Meade, whose wedding the royal couple attended a few weeks ago, and brothers Hugh and William van Cutsem.
Kate’s chief bridesmaid will probably be her sister Pippa, 26, likely to be helped by William’s cousins Zara, 29, Edward’s daughter Lady Louise, six, and Lady Helen Taylor’s daughter Eloise, seven.