They are Oliver Baker, Emilia Jardine-Paterson, Earl Grosvenor, Jamie Lowther-Pinkerton, Julia Samuel, William van Cutsem and Zara Phillips.
Prince William's cousin, Zara, is expecting a baby herself with former England rugby international Mike Tindall.
Mr Oliver Baker
Oliver Baker attended the University of St Andrews with The Duke and Duchess.
Mrs David Jardine-Paterson
Emilia Jardine-Paterson attended Marlborough College with The Duchess.
Earl Grosvenor (Hugh)
Earl Grosvenor is the son of The Duke of Westminster.
Mr Jamie Lowther-Pinkerton
Jamie Lowther-Pinkerton served as Private Secretary to The Duke and Duchess of Cambridge and Prince Harry from 2005-2012 and continues to serve part-time as Principal Private Secretary and Equerry.
The Hon Mrs Michael Samuel
Julia Samuel was a close friend of The Princess of Wales.
Mrs Michael Tindall
Zara Tindall is The Duke of Cambridge's cousin.
Mr William van Cutsem
William van Cutsem is a childhood friend of The Duke of Cambridge.
The Archbishop of Canterbury christened the three-month-old prince at St James's Palace in London.