So far all the smart money has been on Kate  and William’s first-born being a girl.

But the Sunday People can reveal that Prince Harry is telling close friends  the Royal couple are expecting a BOY.

The delighted Prince is so excited about becoming an uncle that he couldn’t  help revealing the sex of the child.

And while The Duke and Duchess of Cambridge have made no official comment  about the baby due in mid-July, Harry has found it hard to keep the secret.

A source close to the Prince told the Sunday People: “Harry has been telling  everyone Wills and Kate are having a boy and how thrilled he is at the prospect  of having a little nephew.

“He said the whole family were excited about it. Apparently Kate has always  wanted a boy.

“They’re really working hard on baby names now and think they have it  sorted.

“But they won’t reveal anything to ­anyone – not even Harry. Of course,  Harry’s been making up crazy suggestions and winding them up too.

“The close inner circle all know that it’s a boy and they’re busily buying  gifts with a boy theme. There will be an awful lot if blue in their house.”

Officially, the Duke and Duchess of Cambridge have refused to divulge the sex  of their new arrival.

But seven-months-pregnant Kate has dropped a couple of hints.

In March she sparked frenzied speculation that made headlines around the  world when she appeared to accidentally suggest that a girl was on the way.

It happened during a walkabout in Grimsby, when Kate was presented with a  teddy by a local well-wisher.

She thanked the woman for the gift and said: “I will take that for my d..” –  and then stopped herself.

A nearby listener said: “You were going to say daughter, weren’t you?”

Kate replied: “No, we don’t know.”

The slip of the tongue sent royal-­watchers into meltdown and bookies  ­hurriedly cut the odds on a baby girl.

But just a few days later Kate gave another clue – this time indicating the  baby could be a boy, when she revealed she had bought a Bugaboo pram in light  blue.

Insiders took that to mean a boy was on the way – because if Kate had not  known the sex of the youngster, she would have gone for a white or beige  colour.

Kate, 31, revealed the pram’s colour when she chatted to a group of Army  wives at a reception on St Patrick’s Day.

A source recalled: “Kate was chatting to them about prams and one of the girls said she had just bought a Bugaboo. Kate said she had as well, a light blue one.”

Prince William’s cousin Princess Eugenie has also been telling friends that  the baby is a boy, according to sources.

But another insider added: “Even though there’s a lot of gossip doing the  rounds, there’s no way anyone can confirm it at the moment.

“It’s people being mischievous and winding each other up.

“Kate and William are really enjoying the speculation but are keen not to  give the game away.”

Another clue appeared to emerge a week ago, when Prince Harry was seen  clutching a blue teddy bear as he walked through Kensington Palace Gardens in  London.

Some took that as a signal the new arrival is going to be a boy.

But a seasoned royal-watcher cleared up the mystery.

It transpired Harry was handed the bear by a little girl while he was on a  tour of Nottingham.

The insider explained: “The bear could have been any colour. It was a really  sweet present – but not any kind of coded message.”

Meanwhile, amid all the speculation, Kate and William have been  ­concentrating on getting ready for their little one’s arrival.

The Royal pair have already ­decorated a nursery for the youngster but  there are no clues in the decor. One insider who has seen the design said: “The  decor has been done but it’s very hard to tell from it what the baby’s sex  is.

“It’s not the most outrageous nursery I’ve ever seen. It’s been done very  simply and very tastefully. There really are no clues in there.”

Kate has not yet decided where she will have her baby. It was expected she  would give birth at St Mary’s hospital in Paddington, West London, where Prince  William and Harry were born.

But some insiders say there is a possibility she will have the child at the  Royal Berkshire Hospital in Reading, near the home of her parents.

Both Kate and her sister Pippa were born at the Royal Berkshire Hospital,  where a £3million birth unit opened last year. A source said: “Kate is going to  be staying with her parents towards the end of her pregnancy. It would make more  sense for her to travel to a hospital nearby rather than head all the way into  London when she goes into labour.”

The medical team delivering the baby will be led by Alan Farthing, the  Queen’s surgeon-gynaecologist.

Kate also plans to stay with her mother and father Carole and Michael  Middleton after the baby is born, breaking with the Royal tradition of moving  straight into Kensington Palace.

She will spend six weeks at their new £4.85million Georgian manor near the  old family home in Bucklebury, Berks. Sources said Kate felt “safest and most  secure” with her family and the Middleton’s have already ­installed a  nursery.

Preparations have been ­under way since the announcement of her pregnancy  in December.

The revelation came after Kate was admitted to a London hospital with severe  morning sickness.

In January, St James’s Palace announced the child would be born in July.

The new arrival will be third in line to the throne – no matter what its  sex.

Read more: Mirror