Prince George, who celebrates his third birthday on July 22, 2016, sits on a picnic blanket while offering an ice cream to the family dog, Lupo, at the family's Norfolk home.

An undated handout photo released by the Duke and Duchess of Cambridge of Prince George, who celebrates his third birthday on July 22, 2016, balancing on a wooden swing, at the family's Norfolk home.

An undated handout photo released by the Duke and Duchess of Cambridge of Prince George, who celebrates his third birthday on July 22, 2016, balancing on a wooden swing, at the family's Norfolk home.

An undated handout photo released by the Duke and Duchess of Cambridge of Prince George, who celebrates his third birthday on July 22, 2016, at the family's Norfolk home.

Prince George gives a thumbs-up as he attends the Royal International Air Tattoo at RAF Fairford, July 8, 2016, in Fairford, England.

Catherine, Duchess of Cambridge, Princess Charlotte, Prince George and Prince William, Duke of Cambridge stand on the balcony of Buckingham Palace during the Trooping the Colour, this year marking the Queen's 90th birthday at The Mall, June 11, 2016, in London.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge, pose with their children, Princess Charlotte and Prince George during a private break skiing at an undisclosed location in the French Alps, March 3, 2016.

Prince George is seen on his way to his first day of nursery school, Jan. 6, 2016.

Prince George is seen on his way to his first day of nursery school, Jan. 6, 2016.

This photo dated July 2, 2014, was taken to mark Prince George's first birthday and shows the Duke and Duchess of Cambridge and the Prince during a visit to the Sensational Butterflies exhibition at the Natural History Museum, London.

This photo dated Wednesday July 2, 2014, was taken to mark Prince George's first birthday and shows the Duke and Duchess of Cambridge and the Prince during a visit to the Sensational Butterflies exhibition at the Natural History Museum, London.

Prince George of Cambridge walks alongside his mother Catherine, Duchess of Cambridge as they watch Prince William, Duke of Cambridge & Prince Harry play in the Jerudong Trophy charity polo match at Cirencester Park Polo Club, June 15, 2014, in Cirencester, England.

Prince William, Duke of Cambridge and Prince George attend the Jerudong Park Trophy at Cirencester Park Polo Club, June 15, 2014, in Cirencester, England.

Australian Prime Minister Tony Abbott looks on as Catherine, Duchess of Cambridge holds Prince George of Cambridge as they leave Fairbairne Airbase to head back to the UK after finishing their Royal Visit to Australia, April 25 2014, in Canberra, Australia.

Prince William, Duke of Cambridge holds Prince George of Cambridge as Catherine, Duchess of Cambridge gives him a toy bilby during a visit to the Bilby Enclosure at Taronga Zoo, April 20, 2014, in Sydney, Australia. The Duke and Duchess of Cambridge are on a three-week tour of Australia and New Zealand, the first official trip overseas with their son, Prince George of Cambridge.

Catherine, Duchess of Cambridge holds Prince George of Cambridge as Prince William, Duke of Cambridge look whilst meeting a Bilby called George at Taronga Zoo, April 20, 2014, in Sydney, Australia.

Prince William, Duke of Cambridge and Prince George of Cambridge visit the Bilby Enclosure at Taronga Zoo, April 20, 2014, in Sydney, Australia.

Catherine, Duchess of Cambridge, Prince William, Duke of Cambridge and Prince George of Cambridge look on before boarding a Royal Australian Air Force plane for their flight to Australia at Wellington Airport's military terminal, April 16, 2014, in Wellington, New Zealand.

Catherine, the Duchess of Cambridge, holds Prince George during a Plunket nurse and parents group visit at Government House in Wellington, April 9, 2014. Plunket is a national not-for-profit organisation that provides care for children and families in New Zealand. Britain's Prince William, Kate and their son Prince George are on a three-week tour of New Zealand and Australia.

Prince George of Cambridge attends Plunkett's Parent's Group at Government House, April 9, 2014, in Wellington, New Zealand. The Duke and Duchess of Cambridge are on a three-week tour of Australia and New Zealand, the first official trip overseas with their son, Prince George of Cambridge.

Catherine, Duchess of Cambridge and Prince George of Cambridge arrive at Wellington Military Terminal, April 7, 2014, in Wellington, New Zealand. The Royal Family have arrived in New Zealand for the first day of a Royal Tour to New Zealand and Australia. Over a period of three weeks the Royal trio will visit 12 Cities in New Zealand and Australia taking part in activities as wide ranging as a yacht race in Auckland Harbour, paying their respects to victims of the 2011 earthquake in Christchurch and visiting Ayres Rock in Australia.

Britain's Prince William and his wife Catherine, carrying baby Prince George, arrive at the international airport in Wellington, April 7, 2014. William, Kate and their son Prince George are on a three-week tour of New Zealand and Australia.

Britain's Prince William, Duke of Cambridge holds his son, Prince George of Cambridge, as he arrives at Chapel Royal in St James's Palace in central London for the christening of the three month-old baby, Oct. 23, 2013. Prince William and his wife Catherine gather close friends and family on Wednesday for the christening of their baby son Prince George, in a low-key ceremony far removed from the global hype surrounding their wedding.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge pose for a photograph with their son, Prince George Alexander Louis of Cambridge, surrounded by Lupo, the couple's cocker spaniel, and Tilly the retriever (a Middleton family pet) in the garden of the Middleton family home, Aug. 2013 in Bucklebury, Berkshire.

Britain's Prince William and Kate, Duchess of Cambridge, hold the Prince of Cambridge, July 23, 2013, as they pose for photographers outside St. Mary's Hospital exclusive Lindo Wing in London.