Princess Charlotte Elizabeth Diana

Princess Charlotte arrives at the Lindo Wing at St. Mary's Hospital in London to visit her mother, Catherine, Duchess of Cambridge, and her newborn brother, Prince Louis, on April 23, 2018.

Princess Charlotte waves as she enters the Lindo Wing at St. Mary's Hospital in London to visit her mother, Catherine, Duchess of Cambridge, and her newborn brother, Prince Louis, on April 23, 2018.

Princess Charlotte arrives with Prince William and Prince George to the Lindo Wing at St. Mary's Hospital in London to visit her mother, Catherine, Duchess of Cambridge, and her newborn brother, Prince Louis, on April 23, 2018.

Princess Charlotte poses at Kensington Palace shortly before her first day of nursery at the Willcocks Nursery School on Jan. 8, 2018.

Princess Charlotte poses at Kensington Palace shortly before her first day of nursery at the Willcocks Nursery School on Jan. 8, 2018.

Princess Charlotte inside a helicopter at Hamburg airport in Germany on July 21, 2017.

Princess Charlotte of Cambridge views helicopter models before departing from Hamburg airport on the last day of an official visit to Poland and Germany on July 21, 2017.

Princess Charlotte at Berlin Tegel Airport in Germany on July 19, 2017.

Princess Charlotte of Cambridge arrives at Berlin Tegel Airport during an official visit to Poland and Germany on July 19, 2017.

Princess Charlotte inside her family's plane at Berlin Tegel Airport in Germany on July 19, 2017.

Princess Charlotte attends the wedding of Pippa Middleton and James Matthews at St. Mark's church in Englefield, England, on May 20, 2017.

A handout picture released by Kensington Palace and Britain's Duke and Duchess of Cambridge on May 1, 2017 and taken by the Duchess shows Princess Charlotte of Cambridge at Anmer Hall in the village of Anmer in Norfolk, eastern England, in April, 2017.

Princess Charlotte of Cambridge leaves following the service at St Mark's Church on Christmas Day on December 25, 2016 in Bucklebury, Berkshire.

Kate, the Duchess of Cambridge and her daughter Princess Charlotte arrive for the morning Christmas Day service at St Mark's Church in Englefield, England, on Sunday Dec. 25, 2016.

Catherine, Duchess of Cambridge and Princess Charlotte leave from Victoria Harbour to board a sea-plane on the final day of their Royal Tour of Canada on October 1, 2016 in Victoria, Canada.

Princess Charlotte leaves from Victoria Harbour to board a sea-plane on the final day of their Royal Tour of Canada on October 1, 2016 in Victoria, Canada.

Princess Charlotte attends a party at Government House in Victoria, British Columbia, Canada, on Sept. 29, 2016.

Kate, Duchess of Cambridge, smiles at Princess Charlotte while she plays with a toy during a children's party in Victoria, British Columbia, on Thursday, Sept. 29, 2016.

Princess Charlotte plays with a dog at a children's party for Military families at Government House in Victoria, British Columbia, Canada, on Sept. 29, 2016.

Catherine, Duchess of Cambridge, and Princess Charlotte watch a man inflate a balloon at a children's party at Government House in Victoria, British Columbia, Canada, on Sept. 29, 2016.

Catherine, Duchess of Cambridge and Princess Charlotte of Cambridge arrive at the Victoria Airport on September 24, 2016 in Victoria, Canada.

Britain's Princess Charlotte poses at Anmer Hall in Norfolk, England, in an undated photo released on Sunday, May 1, 2016.

Britain's Princess Charlotte poses at Anmer Hall in Norfolk, England, in an undated photo released on Sunday, May 1, 2016.

Britain's Princess Charlotte poses at Anmer Hall in Norfolk, England, in an undated photo released on Sunday, May 1, 2016.

Princess Charlotte poses at Anmer Hall in Norfolk, England, in an undated photo released on Sunday, May 1, 2016.

Prince William and Princess Charlotte in the French Alps on Thursday, March 3, 2016.

Princess Charlotte, at Anmer Hall in Sandringham, England.

Princess Charlotte with her cuddly toy dog, at Anmer Hall in Sandringham, England in an undated photo from 2015.

Princess Charlotte after her christening at St. Mary Magdalene Church in Sandringham, England on Sunday, July 5, 2015.

This image made available by Kensington Palace Saturday, June 6, 2015, taken by Kate, Duchess of Cambridge, at Amner Hall, eastern England in mid-May 2015 shows Britain's Princess Charlotte, right, being held by her brother, Prince George.

Prince William and Kate leave St. Mary's Hospital's Lindo Wing in London with their newborn daughter, Charlotte, on Saturday, May 2, 2015.

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge depart the Lindo Wing with their newborn daughter, Charlotte, at St Mary's Hospital on May 2, 2015 in London, England.

Princess Charlotte Elizabeth Diana, daughter of Prince William and Kate was born at Mary's Hospital in London, on Saturday, May 2, 2015.

Charlotte Elizabeth Diana, daughter of Britain's Prince William and Kate, Duchess of Cambridge, is all bundled up to leave St. Mary's Hospital in London on Saturday, May 2, 2015.