Prince William and Kate Middleton have revealed that their third child will be born in April - meaning the baby could have been conceived during a Royal tour.

The Duke and Duchess of Cambridge went on a five-day tour of Germany and Poland in the middle of July this year.

The couple landing in Warsaw on July 16 with Prince George and Princess Charlotte, who were being looked after by their Spanish nanny.

Today, Kensington Palace announced the Duchess will give birth in April - nine months after the tour took place.

William and Kate's trip, taken at the request of the Foreign and Commonwealth Office, was seen as another Brexit diplomacy, helping to maintain and strengthen the UK's relations with Europe as it leaves the EU.

But during one event Kate appeared less than happy with her husband.

Kate appeared less than impressed during one night out (
Image:
Splash News)
The Duchess may have conceived during the tour of Poland and Germany (
Image:
Splash News)
During one event Kate appeared furious with her husband (
Image:
Splash News)

The Duke and Duchess of Cambridge cut a miserable figure as they were snapped leaving their residence while heading to a Warsaw garden party - marking the Queen's birthday- on April 17.

Looking less than impressed, Kate Middleton appeared to scowl as she left the building and made her way towards a waiting car.

The family went on a five-day tour of Poland and Germany (
Image:
PA)
Kate and Charlotte arrive in Berlin (
Image:
PA)

Her demeanour seemed drastically different to her beaming smiles and jovial chats to crowds outside Poland's Presidential Palace just hours before.

Without looking Prince William in the eye the mum-of-two largely kept her head down before managing to crack a faint smile towards cameras. William too seemed eager to get to their waiting car, a stern look etched across his face.

The couple arrive for a reception at 'Claerchens Ballhaus' dance hall in Berlin (
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AFP)
Kate Middleton is about three months pregnant (
Image:
Getty Images Europe)

During the trip the family stayed at the Belweder Palace in Warsaw before moving on to the British ambassador to Germany's residence in Berlin.

The Royal couple's first full day began with a trip to the former Nazi Germany Concentration Camp, Stutthof.

But they also visited museums, research centres and a German dancehall.

The Duke and Duchess of Cambridge are said to be 'delighted' at having a third baby after Prince George and Princess Charlotte.

A short statement from Kensington Palace said: "Their Royal Highnesses The Duke and Duchess of Cambridge are delighted to confirm they are expecting a baby in April 2018."

The news comes more than a month after Kate's pregnancy was first announced, although the exact due date of the baby's arrival has not been revealed.

The baby will be fifth-in-line to the British throne, pushing uncle Prince Harry into sixth place.