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Duke and Duchess of Cambridge expecting third child

Composite image of Royal family, and Prince George and Princess Charlotte in their younger years.PA/Reuters

The family of four are set to become five, with a new baby on the way.

Prince William and the Duchess of Cambridge are expecting their third child.

Buckingham Palace told everyone the news on Monday morning, adding that the Queen is "delighted".

It'll make it a big week for Kensington Palace, with four-year-old Prince George due to start school on Thursday.

Now he and two-year-old Princess Charlotte can get used to the idea of having a future new brother or sister as well!

Catherine, Duchess of Cambridge, (L) and Prince William posing for pictures with their new baby son Prince George. Britain's Prince William and his wife Kate have named their new baby boy George Alexander Louis, Kensington Palace announced on Wednesday July 24, 2013. "The Duke and Duchess of Cambridge are delighted to announce that they have named their son George Alexander Louis.AFP/Getty Images

Prince George was born on 22 July 2013 at St Mary's Hospital in London.

William and Kate's third child will become the fifth person in line to the throne.

This is the line of people who could go on to be King or Queen.

The new child will be behind their granddad, Prince Charles, dad, Prince William, and siblings Prince George and Princess Charlotte.

If it is a boy, Charlotte will be the first girl to be ahead of their brother in the line to the throne.

This is because of new rules that started in 2015.

Britain"s Prince William and his wife Catherine, Duchess of Cambridge, appear with their baby daughter outside the Lindo Wing of St Mary"s Hospital, in London, Britain May 2, 2015Reuters

Princess Charlotte joined the Royal family almost two years later on 2 May 2015.

Britain's Prince William, Duke of Cambridge (L) and Catherine, Duchess of Cambridge (2-R) walk with their children Prince George (2-L) and Princess Charlotte during a farewell ceremony at the airport after visiting the Airbus Factory in Hamburg, Germany, 21 July 2017EPA

Prince George and Princess Charlotte often travel with their parents, so the new baby could join them on foreign engagements in the future as well.

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