The Queen had to grant special permission for Prince William and Kate Middleton to go on holiday as a family.

The Duke and Duchess of Cambridge, both 39, were seen at Gatwick Airport with their children as they travelled for half term to an undisclosed location.

The royals were seen outside the Windsor Suite, which is reserved for the Royal Family and other high profile celebrities, with Prince George, eight, Princess Charlotte, six and Prince Louis, three.

The royals have undertaken several holidays together, including royal tours to Canada, Poland and Germany.

But the latest break may be one of the last times the family travels as a group, CornwallLive reports.

Due to a set of strange rules created to protect the Royal lineage, senior members of the family are often not allowed to fly together unless their journey is approved by Her Majesty.

Prince William was spotted outside the Windsor Suite at Heathrow along with his wife the Duchess of Cambridge and their three children last week (

Image:

SWNS)

With the Cambridge family heading abroad, it was questioned whether the rule would come into play.

When George turns 12, he will be required to fly separately from his father.

This is because William and George are second and third in line to the throne respectively, which means they must travel separately in case something tragic happens during their journey.

The rule also forbids Charles and William from flying together, as well as Charles and the Queen.

In the past, the Cambridges have flown with their children.

The Cambridges have previously travelled together to different parts of the world but it's unsure for how long they will be able to (

Image:

Getty)

William was granted special permission from the Queen to bend these rules when his son was nine months old and the family travelled to Australia and New Zealand in 2014.

In addition, the Queen granted permission to the couple in September 2016, when they travelled with George and Charlotte to Canada.

The Cambridges flew together again during a tour to Poland and Germany in July 2017 - taking a total of three flights together.

William and Kate won't be able to travel with George when he turns 12 as it is unlikely anymore exceptions to the rule will be made then (

Image:

Getty)

However, the family appears to have sometimes followed the rule in the past, for example in December 2014 when they travelled to New York.

Their young son remained at home with his nanny and grandmother Carole Middleton.

William is not technically allowed to travel with any of his children given their high position on the line of succession.

The Royal Family’s press office told Newsround: “They had to ask the Queen for permission, but she said yes.

"While there is no official rule on this, and royal heirs have travelled together in the past, it is something that the Queen has the final say on."

It's not known where the family have been visiting, but many believe they may have flown to Greece for the wedding of Princess Diana's godson Prince Philippos and Nine Flohr.

The family have been known to holiday in locations including the Isles of Scilly, Lake District and their Norfolk home, Anmer Hall.

They were joined at the airport by their nanny Maria Teresa Turrion Borrallo at the airport.

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