Prince William broke with royal convention by naming his cousin, the champion horserider Zara Phillips, and six old friends as godparents to his son Prince George ahead of the baby’s private christening on Wednesday.

Three-month-old George, the first child of William and his wife Kate, was set to be christened at St James’s Palace in London in a low-key ceremony attended only by close family members, the godparents and their spouses.

Zara, who is herself pregnant with her first child with her rugby player husband Mike Tindall, is the only family member named godparent to George in a statement released by William and Kate’s residence Kensington Palace ahead of the service.

The others are close friends of the couple including Jamie Lowther-Pinkerton, a former soldier in the elite SAS army unit who is William’s principal private secretary, and Oliver Baker, a friend from their time at St Andrew’s University in Scotland, where they first met.

William van Cutsem, a childhood friend of William’s, is also on the list along with Emilia Jardine-Paterson, a school friend of Kate’s who now works as an interior decorator.

The final two godparents are Hugh Grosvenor — whose mother, the Duchess of Westminster, is William’s own godmother — and Julia Samuel, a close friend of William’s late mother Princess Diana.

The choice of godparents marks a break from the British monarchy’s tradition of including relations from foreign royal families on the list.

William has six godparents, including king Constantine II of Greece, while his father Prince Charles counts king Haakon of Norway and Prince George of Greece and Denmark among his godfathers.

A total of 22 guests are attending Wednesday’s ceremony including Queen Elizabeth II and Kate’s parents, Michael and Carole Middleton, the palace said in a statement.