The Duke and Duchess of Cambridge are to take a nanny on their trip to Australia and New Zealand to care for Prince George on his first royal tour, Kensington Palace has announced.

The nanny, who has not been named, will accompany William and Kate on their visit to New Zealand and Australia in April to look after their son while they carry out official duties, a spokesman said.

Palace officials would not confirm who the nanny is but the couple may opt to take William's former nanny Jessie Webb who has been helping the Cambridges with child care duties on an ad hoc basis.

The baby will be eight months old when he flies Down Under with his parents on his first official overseas tour.

The three week visit will echo the Prince and Princess of Wales's visit to Australia and New Zealand in 1983 when the couple took William, then just nine months old, with them.

The little Prince will be seen in public at least four times when he embarks and disembarks aircraft. It is hoped that he will also attend a couple of events on the tour, one in each country, though officials said confirmation of his attendance will be made closer to the time.

The visit could see the first time that the third-in-line to the throne is left overnight without either of his parents - the couple are planning a two-day trip in New Zealand without the youngster.

Miguel Head, the Duke of Cambridge's private secretary, said: "The party is similar in size to recent overseas visits undertaken by Their Royal Highnesses.

"A new addition to the party is, of course, Prince George's nanny."

He confirmed that the couple will not source a local nanny abroad but will take someone from the UK.

On bringing the baby on the tour, he said: "Like any new parents they wanted to ensure that the decision was theirs and it wasn't driven by any other people's expectations.

"They have come to the decision because it is a long way to go and for a long time - three and a half weeks including the travel - and it's a decision that they feel comfortable with."

He added: "One or two engagements across the three weeks have been identified as times when the Duke and Duchess might take Prince George along too. But I'm sure you will appreciate that the couple will have to make a final decision on those moments much closer to the time.

"The Duke and Duchess are content enough to know that he will be with them in the two countries."

The Queen has given approval for William and George to travel together on the trip - they would not have been permitted to travel together without her say so.

"Her Majesty has given permission for it to happen," Mr Head said.

"Indeed Prince William travelled with his parents when he was a very similar age so there is precedent for this."

Officials confirmed that the programme of events has been tailored to accommodate for the fact that the couple have a small child with them.

Mr Head said the Cambridges had planned a "hub and spoke" system by largely basing themselves in three locations - Wellington, New Zealand and Sydney and Canberra in Australia - and visiting various parts of the countries before returning to stay with their son.

"That's so that Prince George doesn't have to move around and the couple can cover as much as they can," he said.

William has travelled to Australia and New Zealand a number of times but Kate has yet to pay an official visit - although she and her husband created a stir last September when they flew to Brisbane airport to catch a flight home at the end of their South Pacific tour.

The second-in-line to the throne has said he wishes to show his wife the two countries - which have close ties with the UK.

Mr Head said: "There is no hiding the enthusiasm for this visit by both the Duke and The Duchess. The Duke, because he has been before and the Duchess because she has never been to either country but has wanted to do so as long as she can remember.

"The Duke has no doubt that his wife will fall in love with New Zealand and Australia every bit as much as he did, some years ago."

He added: "It's a tremendously exciting visit and I can tell you Their Royal Highnesses are looking forward to it immensely."

The trip, which will start in just over five week's time, will end on Friday April 25 - just four days before the Duke and Duchess celebrate their third wedding anniversary.

The Duke's last official trip to New Zealand and Australia was in March 2011, when he visited Christchurch, shortly after it suffered an earthquake, and the Australian states of Queensland and Victoria, which had been hit by floods.

In January 2010 he represented the Queen at the opening of the Supreme Court building in the New Zealand capital Wellington and also visited Auckland, and during the same trip travelled to Melbourne and Sydney.

The latest action-packed tour reflects "outdoorsy and sporty" people that William and Kate are, Mr Head said.

There are an eclectic mix of events including a trek around Ayers Rock, white-water rafting and meeting some of the Rugby World Cup champions All Blacks. The couple will also participate in a boat race - on opposing teams.

"As everyone knows the couple are just a little competitive," Mr Head said.

They will also meet Sir Peter Jackson, maker of the Lord of the Rings and The Hobbit trilogies.

But the visit also includes more formal events with politicians and military personnel - though there are no black tie occasions.

And no royal tour would be complete without the ceremonial planting of a tree.

Kate will also visit children's hospices in each country - continuing her charitable interest in palliative care for youngsters.

In New Zealand the royals will visit Wellington, Auckland and Christchurch among others.

Australia highlights include Sydney, Brisbane, Adelaide and Canberra - but not Melbourne or Perth.

The royal entourage will also include a hairdresser and a personal assistant.

Rebecca Deacon, Kate's private secretary, Mr Head, three press officers, a tour secretary, an orderly and adviser Sir David Manning will also attend.