The Duke and Duchess of Sussex at the christening of their son, Archie Harrison Mountbatten-Windsor at Windsor Castle, July 6, 2019.

Britain's Princess Charlotte poses for a photo taken by her mother, Catherine, Duchess of Cambridge, at their home in Norfolk, Britain in April and released May 1, 2019, to mark her fourth birthday.

Britain's Princess Charlotte poses for a photo taken by her mother, Catherine, Duchess of Cambridge, at their home in Norfolk, Britain in April and released May 1, 2019, to mark her fourth birthday.

This photo released by Kensington Palace on Monday April 22, 2019, and taken by Kate, Duchess of Cambridge, shows Prince Louis at their home in Norfolk, England, to mark his first birthday on April 23.

Prince George poses for a picture following the christening of his brother Prince Louis, at Clarence House in London, July 9, 2018. Prince William and Kate, Duchess of Cambridge have released a photo of Prince George to mark his fifth birthday on July 22.

Princess Charlotte, Catherine, Duchess of Cambridge and Prince George attend the Maserati Royal Charity Polo Trophy at Beaufort Park, June 10, 2018, in Gloucester, England.

Prince George and Princess Charlotte of Cambridge run together during the Maserati Royal Charity Polo Trophy at Beaufort Park, June 10, 2018, in Gloucester, England.

Princess Charlotte waves while holding her mother Catherine, the Duchess of Cambridge's hand after attending the wedding ceremony of Prince Harry and Meghan Markle at Windsor Castle, in Windsor, May 19, 2018.

Britain's Prince George leaves after the wedding of Prince Harry and Meghan Markle at St. George's Chapel in Windsor Castle in Windsor, May 19, 2018.

Catherine, the Duchess of Cambridge arrives with the bridesmaids at St George's Chapel at Windsor Castle for the wedding of Prince Harry and Meghan Markle in Windsor, May 19, 2018.

Duchess of Cambridge shows her daughter Princess Charlotte kissing her newborn brother Prince Louis on her third birthday in London, May 2, 2018.

Prince Louis three days after he was born at Kensington Palace on April 26, 2018, in London.

Princess Charlotte of Cambridge turns to wave at the media as she goes with her brother Prince George and their father, Prince William, at the Lindo Wing of St Mary's Hospital to meet their newborn brother in central London, April 23, 2018.

Catherine, Duchess of Cambridge, holds her newborn son as she and her husband, Prince William, Duke of Cambridge, show him to the media outside the Lindo Wing at St Mary's Hospital, April 23, 2018, in London. <br><br> Louis Arthur Charles, the third child of William and Kate, weighed 8 pounds, 7 ounces at birth. He was born at 11:01 a.m., local time. <br><br> Prince Louis is fifth in line for the throne.

Princess Charlotte stands on the steps at Kensington Palace shortly before she left for her first day at the Willcocks Nursery School, Jan. 8, 2018.

Two-year-old Princess Charlotte arrives with her royal family at the Tegel Airport in Berlin, July 19, 2017. <br><br> The royal family traveled on a five-day tour of Poland and Germany.

Princess Charlotte to mark her second birthday on May 2, 2017.

Princess Charlotte smiles, at Anmer Hall, in Norfolk, England. The princess will celebrate her first birthday on May 2, 2016.

Princess Charlotte, right, being held by her brother 2-year-old Prince George at Anmer Hall, eastern England in mid-May 2015.

Catherine, Duchess of Cambridge, and Prince William, Duke of Cambridge, depart the Lindo Wing with their newborn daughter at St Mary's Hospital on May 2, 2015, in London. <br><br> Their newborn daughter's name is Charlotte Elizabeth Diana. The second child of William and Kate weighed 8 pounds, 3 ounces at birth. She was born at 8:34 a.m., local time. <br><br> Charlotte is fourth in line to the throne.

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.

Prince George will celebrate his third birthday on July 22, 2016.

Two-year-old Prince George heads to his first day of nursery school, Jan. 6, 2016.

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

Prince George sits for his official Christmas picture in a courtyard at Kensington Palace in late November 2014 in London.

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

Prince George plays during a visit to Plunket nurse and parents group at Government House in Wellington, New Zealand, April 9, 2014.

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 George's christening, Oct. 23, 2013.

Catherine, the Duchess of Cambridge, carries her newborn son Prince George outside St. Mary's Hospital, in London, July 23, 2013. <br><br> Their newborn son's full name is George Alexander Louis. He weighed 8 pounds, 6 ounces at birth and was born at 4:24 p.m., local time. <br><br> George is third in line to the throne.