James , Viscount Severn is the only son of Prince Edward and Sophie , Countess of Wessex .
James , Viscount Severn - James Alexander Philip Theo Mountbatten-Windsor - ( born 17 December 2007 ) is the youngest of the three sons of Prince Edward , Earl of Wessex , and Sophie , Countess of Wessex , and the youngest grandchild of Queen Elizabeth II and Prince Philip , Duke of Edinburgh .