Duchess Catherine's royal gynecologist has postponed his retirement to deliver her third baby.

Duchess Catherine and Prince William

Duchess Catherine and Prince William

The 35-year-old royal and her husband Prince William are set to welcome their little one into the world in April and her 54-year-old doctor Alan Farthing - who delivered her son George in 2013 and daughter Charlotte in 2015 - has agreed to help the brunette beauty with the birth.

A source told Us Magazine.com: "He's postponed his retirement to do it."

And the couple have already reserved a suite in the exclusive Lindo Wing of London's St. Mary's Hospital - where their other two children were born - in preparation for the labour.

Although Catherine still has six months to go until her baby is due, she and William - who got married in 2011 - have started explaining to George and Charlotte that they're getting a sibling.

The insider added: "They know mummy is carrying another brother or sister for them and they're excited. They keep asking about the size of the baby and whether it's a boy or a girl."

And they're starting to fill up the baby's nursery with "hand-me-down clothes and toys."

The insider said: "It's full with hand-me-down clothes and George and Charlotte's old toys."

The couple were forced to announce their pregnancy before the three-month mark after Catherine missed George's first day at school in September because of severe morning sickness - something she suffered with during her first and second pregnancy as well.

The source explained: "They're taking each day as it comes. After you've had two children, the third usually feels like somewhat of a breeze so they're just focused on Kate and the baby's health right now. Everything else can wait."

But she's said to be feeling a lot better and is starting to return to her royal duties.

The source added: "She is feeling significantly better. Especially when you compare to how bad she was at the start. It was a worrying time for everyone."

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