Britain's Prince William (L), Duke of Cambridge stands next to his wife Catherine (R), Duchess of Cambridge who holds their newborn son outside the Lindo Wing at St. Mary's Hospital, 23 April 2018. (EPA/WILL OLIVER)
The newborn son of Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge as they depart the Lindo Wing at St. Mary's Hospital on April 23, 2018 in London, England. (Chris Jackson/Getty Images)
Britain's Catherine, Duchess of Cambridge holds her newborn son outside the Lindo Wing at St. Mary's Hospital in Paddington, London, Britain, 23 April 2018. (EPA/ANDY RAIN)
Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge depart the Lindo Wing with their newborn son at St. Mary's Hospital on April 23, 2018 in London, England. (Chris Jackson/Getty Images)
Britain's Catherine, Duchess of Cambridge holds her newly-born son outside the Lindo Wing at St Mary's Hospital, London, on April 23, 2018. (AFP / John Stillwell)
Princess Charlotte of Cambridge (R) is led in with her brother Prince George of Cambridge (L) by their father Britain's Prince William, Duke of Cambridge, (C) at the Lindo Wing of St Mary's Hospital in central London, on April 23, 2018, to visit Catherine, Duchess of Cambridge, and their new-born brother. (AFP / Daniel LEAL-OLIVAS)
Princess Charlotte of Cambridge (L) turns to wave at the media as she is lead in with her brother Prince George of Cambridge (R) by their father Britain's Prince William, Duke of Cambridge, (C) at the Lindo Wing of St Mary's Hospital. (AFP / Ben STANSALL)
Britain's Prince William arrives with Princess Charlotte at the Lindo wing at St Mary's Hospital in London, April 23, 2018. (AP / Kirsty Wigglesworth)
Prince William, Duke of Cambridge, leaves the Lindo Wing of St Mary's Hospital after Catherine, Duchess of Cambridge, gave birth to a baby boy on April 23, 2018 in London, England. (Jack Taylor/Getty Images)
Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge, show off their newborn son outside St Mary's Hospital on April 23, 2018 in London, England. (Gareth Cattermole/Getty Images)
Britain's Catherine, the Duchess of Cambridge and Prince William leave the Lindo Wing of St Mary's Hospital with their new baby boy in London, April 23, 2018. (REUTERS/Henry Nicholls)
A notice is placed on an easel in the forecourt of Buckingham Palace to formally announce the birth of a baby boy to the Britain's Catherine, the Duchess of Cambridge, and Prince William, in London, April 23, 2018. (Stefan Rousseau/ Reuters)
Senior footman Olivia Smith and footman Heather McDonald place a notice on an easel in the forecourt of Buckingham Palace to formally announce the birth of a baby boy to the Britain's Catherine, the Duchess of Cambridge, and Prince William, in London, April 23, 2018. (Stefan Rousseau/ Reuters)
A general view of the BT Tower as it announces the birth of Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge's newborn son on April 23, 2018 in London, England. (Jeff Spicer/Getty Images)
The London Eye is illuminated red, white and blue to show support for the The Duke and Duchess of Cambridge as they welcome their new baby son on April 23, 2018 in London, England. (John Phillips/Getty Images)
Royal well-wishers celebrate the birth of a baby boy outside the Lindo Wing of St. Mary's hospital in London, Britain, 23 April 2018. (EPA/ANDY RAIN)
A traditional town crier announces the birth of a baby boy outside the Lindo Wing of St. Mary's hospital in London, Britain, 23 April 2018. (EPA/ANDY RAIN)
Royal well-wishers hung a sign outside the Lindo Wing of St. Mary's hospital in London, Britain, 23 April 2018. (EPA/ANDY RAIN)
Royal fans pose outside the private Lindo Wing of St Mary's Hospital, in central London. (AFP / Daniel LEAL-OLIVAS)
Britain's Prince William (L), Duke of Cambridge stands next to his wife Catherine (R), Duchess of Cambridge who holds their newborn son outside the Lindo Wing at St. Mary's Hospital, 23 April 2018. (EPA/WILL OLIVER)
The newborn son of Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge as they depart the Lindo Wing at St. Mary's Hospital on April 23, 2018 in London, England. (Chris Jackson/Getty Images)
Britain's Catherine, Duchess of Cambridge holds her newborn son outside the Lindo Wing at St. Mary's Hospital in Paddington, London, Britain, 23 April 2018. (EPA/ANDY RAIN)
Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge depart the Lindo Wing with their newborn son at St. Mary's Hospital on April 23, 2018 in London, England. (Chris Jackson/Getty Images)
Britain's Catherine, Duchess of Cambridge holds her newly-born son outside the Lindo Wing at St Mary's Hospital, London, on April 23, 2018. (AFP / John Stillwell)
Princess Charlotte of Cambridge (R) is led in with her brother Prince George of Cambridge (L) by their father Britain's Prince William, Duke of Cambridge, (C) at the Lindo Wing of St Mary's Hospital in central London, on April 23, 2018, to visit Catherine, Duchess of Cambridge, and their new-born brother. (AFP / Daniel LEAL-OLIVAS)
Princess Charlotte of Cambridge (L) turns to wave at the media as she is lead in with her brother Prince George of Cambridge (R) by their father Britain's Prince William, Duke of Cambridge, (C) at the Lindo Wing of St Mary's Hospital. (AFP / Ben STANSALL)
Britain's Prince William arrives with Princess Charlotte at the Lindo wing at St Mary's Hospital in London, April 23, 2018. (AP / Kirsty Wigglesworth)
Prince William, Duke of Cambridge, leaves the Lindo Wing of St Mary's Hospital after Catherine, Duchess of Cambridge, gave birth to a baby boy on April 23, 2018 in London, England. (Jack Taylor/Getty Images)
Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge, show off their newborn son outside St Mary's Hospital on April 23, 2018 in London, England. (Gareth Cattermole/Getty Images)
Britain's Catherine, the Duchess of Cambridge and Prince William leave the Lindo Wing of St Mary's Hospital with their new baby boy in London, April 23, 2018. (REUTERS/Henry Nicholls)
A notice is placed on an easel in the forecourt of Buckingham Palace to formally announce the birth of a baby boy to the Britain's Catherine, the Duchess of Cambridge, and Prince William, in London, April 23, 2018. (Stefan Rousseau/ Reuters)
Senior footman Olivia Smith and footman Heather McDonald place a notice on an easel in the forecourt of Buckingham Palace to formally announce the birth of a baby boy to the Britain's Catherine, the Duchess of Cambridge, and Prince William, in London, April 23, 2018. (Stefan Rousseau/ Reuters)
A general view of the BT Tower as it announces the birth of Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge's newborn son on April 23, 2018 in London, England. (Jeff Spicer/Getty Images)
The London Eye is illuminated red, white and blue to show support for the The Duke and Duchess of Cambridge as they welcome their new baby son on April 23, 2018 in London, England. (John Phillips/Getty Images)
Royal well-wishers celebrate the birth of a baby boy outside the Lindo Wing of St. Mary's hospital in London, Britain, 23 April 2018. (EPA/ANDY RAIN)
A traditional town crier announces the birth of a baby boy outside the Lindo Wing of St. Mary's hospital in London, Britain, 23 April 2018. (EPA/ANDY RAIN)
Royal well-wishers hung a sign outside the Lindo Wing of St. Mary's hospital in London, Britain, 23 April 2018. (EPA/ANDY RAIN)
Royal fans pose outside the private Lindo Wing of St Mary's Hospital, in central London. (AFP / Daniel LEAL-OLIVAS)
Britain's Prince William (L), Duke of Cambridge stands next to his wife Catherine (R), Duchess of Cambridge who holds their newborn son outside the Lindo Wing at St. Mary's Hospital, 23 April 2018. (EPA/WILL OLIVER)