Royal baby's arrival and name will keep the bookies occupied

Prince William and Catherine, Duchess of Cambridge. Photo / AP

The Duchess of Cambridge is pregnant with her third child, a sibling for Prince George and Princess Charlotte - but when will the latest family member arrive?

While most parents don't announce the happy news until the crucial 12-week stage, the Duchess is suffering from hyperemesis gravidarum, or severe morning sickness, a condition that is usually detected around the six-week mark.

When pregnant with Princess Charlotte, the Duchess had to announce the news early after the condition forced her to pull out of planned engagements and today's announcement from Kensington Palace came as she cancelled a planned visit to a children's charity in London this afternoon, according to Daily Mail.

Assuming Kate is around six to eight weeks pregnant, the new arrival can be expected in late April or early the following month, around the time of Princess Charlotte's birthday on May 2.

And a new family member around the end of April would be a delightful wedding present for Kate and William, who will celebrate seven years of marriage on the 29th.

The couple will also be busy considering baby names in the next months, with bookies Ladbrokes already taking bets on a moniker for the new arrival and a girl called Alice the favourite at 7/1.

Alice was the name of one of Queen Victoria's daughters and also of the Duke of Edinburgh's mother.

Arthur and Victoria are the next joint favourite at 10/1, followed by Alexander and Alexandra, both at 12/1.

The bookies make it even money George and Charlotte are joined by a sister, and the same price is on offer for a brother.

Either way, the couple will keep it classic just like they did for Prince George and Princess Charlotte, but as the new baby will be fifth in line to the throne there's no pressure to name them after a past monarch like big brother and future king, Prince George.

Catherine Duchess of Cambridge and Princess Charlotte of Cambridge during an official visit to Poland and Germany on July 19, 2017 in Berlin, Germany. Photo / Getty Images

Philip is another strong contender for a boy, in honour of the baby's great-grandfather the Duke of Edinburgh who will turn 97 shortly after the birth.

Other suggestions include Alexandra or Mary, the Queen's two middle names and the names of her grandmother Queen Mary and great-grandmother Queen Alexandra - or Amelia, the name of one of George III's daughters.

Born in 1783, Amelia was the youngest of the king's 15 children. She fell passionately in love with one of her father's equerries, Charles Fitzroy, but was forbidden by her mother from marrying him. She died from tuberculosis when she was just 27.

George II also had a daughter called Amelia. The name has been the most popular girls' name in England and Wales since 2011.

Isabella could also be a contender. There is a young Princess Isabella of Denmark, who was born in 2007.

Elizabeth - after the baby's great-grandmother the Queen - has already been used as one of Charlotte's middle names, as has Diana in remembrance of William's late mother. Dorothy might be selected as a middle name in tribute to Kate's maternal grandmother.

Historically royal names such as James - also the name of Kate's brother - are among the favourite predictions for a boy.

Other contenders could be Charles, to honour the Prince of Wales, Albert, Arthur, Frederick or even Henry - Prince Harry's actual name.

Francis is a family name for the Middletons, while Diana, Princess of Wales' middle name was Frances. A middle name tribute might be made to Kate's father Michael, or her paternal grandfather Peter.

Both George and Charlotte have two middle names - George's are Alexander and Louis - so the new addition to the family is also likely to be given two.

William and Kate chose Alexander as a second name for George simply because they liked the name, and they went for Louis in memory of Charles' beloved late great-uncle, Lord Louis Mountbatten.

Prince William, Duke of Cambridge, Prince George of Cambridge, Princess Charlotte of Cambridge and Catherine, Duchess of Cambridge depart from Hamburg airport. Photo / Getty Images

Like they did previously, William and Kate will wait until the Queen has been informed of the baby's name before they announce it to the world.

The bookmakers have set the chance that Kate has twins at 4-1.

Coral spokesman David Stevens said: "Late last month we had to cut the odds on the royal couple announcing this news to 1-2 from 3-1, and that gamble has proved to be spot on.

"It's cost us a few quid but we'll be paying out with a smile after this good news."

He added: "Alice is the early favourite when it comes to the potential name of the royal new arrival, while Diana at 14-1 could prove popular with punters."

Paddy Power also has Alice as the favourite at 8-1, with Arthur at 10-1 and Diana at 20-1.

A Paddy Power spokesman said: "Given the recent anniversary, there'll be plenty of interest in the name Diana if the baby is a girl."

William Hill has Alice as the 8-1 favourite, with Elizabeth and James both at 10-1. With US leader Donald Trump in charge of the White House, Donald is at 50-1.

Joe Crilly, William Hill spokesman, said: "Royal baby betting is big business and when Prince George was born, we took over £1 million [$1.8m]. Turnover looks set to spike again.

"Most of the names towards the top of the betting are ones which have been popular the last two times around and we expect they will be again."

William Hill set the odds of royal twins at 33-1.

"Last time around, twins was very heavily backed from 33-1 in to 10-1 and it would be no surprise to see the same thing happen this time," said Crilly.

The happy news that George, 4, and Charlotte, 2, will have a new sibling next year came later via Kensington Palace, who said in a statement: "Their Royal Highnesses the Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting their third child".

The Queen, Prince Charles, the Duchess of Cornwall and other members of both families are delighted with the news.

The child will be fifth in line to the throne, bumping Prince Harry into sixth place.