Duchess of Cambridge pregnant: Kate to have second royal baby next year
A second royal baby is on the way as Kensington Palace announces the Duchess of Cambridge is pregnant.
The Queen and members of both William and Kate's families are "delighted" with the news, Kensington Palace said.
The palace also said the Duchess was suffering from acute morning sickness, as she did when when pregnant with Prince George.
Prime Minister David Cameron congratulated the Duke and Duchess on the news of a second child.
Just days before Scotland is due to vote on independence, First Minister Alex Salmond also sends congratulations to future King and Queen.
Kate was due to join William in formally opening Oxford University's £21 million centre dedicated to the study of China. He will still attend, as planned, Kensington Palace said.
The announcement that the couple are expecting their second child comes two months after Prince George turned one.
The third-in-line to the throne was born on July 22 last year to a worldwide fanfare.
Kate suffered with hyperemesis gravidarum with her last pregnancy and is suffering from the very acute morning sickness again, meaning she may need extra hydration, medication and nutrients.
The couple's second child will become fourth in line to the throne, shifting Prince Harry further down the line of succession.
The Duchess of Cambridge's announcement will throw into doubt whether she will be able to attend her first solo overseas tour, set to take place in Malta later this month.
Kate is said to be suffering from acute morning sickness, as she did with her first pregnancy, and is being treated by doctors at Kensington Palace. She is no longer joining her husband on a planned engagement in Oxford today.
Prime Minister David Cameron offered his congratulations to the couple today, saying: "Many congratulations to the Duke and Duchess of Cambridge. I'm delighted by the happy news that they're expecting another baby."
With just 10 days to go before the Scottish independence vote, First Minister Alex Salmond also congratulated the royal couple.
"This is very happy news for any couple, and on behalf of the people of Scotland, I am delighted to send our best wishes to the Countess and our hearty congratulations to the royal couple.", he said.
The Duchess is known in Scotland as the Countess of Strathearn.
'Spare to the heir' is a tough role - just ask Andrew, Harry and Margaret
The "spare to the heir" is often a difficult role to fulfil within the Royal Family.
Second-born royals are characteristically less cautious and enjoy the freedom that comes with not having to prepare to rule as monarch.
But the position is open to criticism as the privileged and sometimes troublesome younger sibling to a future sovereign attempts to carve out a life for themselves amid the scrutiny of being an HRH.
Prince Harry, the Duke of York and the late Princess Margaret were all spares to the heirs and each encountered criticism over their conduct.
Now the Duke and Duchess of Cambridge's second child will be born as next in line after an older sibling and grow up in the same position.
Unlike Prince George, this Prince or Princess will be free from the responsibility of one day having to become monarch.
Whereas George is expected to eventually become king, as well as head of the armed forces and the Church of England, and possibly head of the Commonwealth, the younger Cambridge sibling is likely to have a less restrictive future.
Prince Harry has traditionally been dubbed a party prince in contrast to his older brother William - a future king. It is Harry who has scuffled with paparazzi photographers and been pictured naked playing strip billiards in Las Vegas.
As a child, Harry was always the more mischievous of the two princes.
Royal writer Christopher Warwick compared the brothers to the Queen and her younger sister Princess Margaret.
"William and Harry are the Elizabeth and Margaret of this generation. William is the dedicated, dutiful one who will perhaps one day be king. The other sibling, like Margaret, who didn't have these responsibilities and duties, can pursue a different type of private life," Mr Warwick said.
As a child, Princess Elizabeth was sensible and responsible, while Princess Margaret Rose was vivacious, naughty and fun.
Margaret, who died in 2002, was known for her glamorous lifestyle and turbulent love life. In the 1950s she fell in love with the divorced Group Captain Peter Townsend but renounced him after coming under political, family and church pressure.
She wed and later divorced photographer Antony Armstrong-Jones, who became Lord Snowdon, and went on to have an affair for several years in the 1970s with Roddy Llewellyn, who was 17 years younger.
The Duke of York, who until the arrival of William in 1982 had been next in line after the Prince of Wales, has also faced controversy.
He is nicknamed Air Miles Andy because of his jet-setting and frequent use of helicopters and his suitability as the UK special representative for trade and investment was criticised throughout his 10 years in the role.
Prince Harry slips down to fifth place with George's sibling to become fourth in line to the throne
The new royal baby will be born fourth in line to the throne. As a sibling to Prince George, the Duke and Duchess of Cambridge's second child will not be expected to be crowned sovereign.
But second-born royal children - often dubbed the "spare to heir" - have on occasion ended up as monarch.
The country's last king, George VI, was not meant to accede to the throne and only did so when his older brother Edward VIII abdicated over his love for American divorcee Wallis Simpson in 1936.
George VI's father, George V, was also not destined to wear the crown. But he outlived his older brother the Duke of Clarence and Avondale - Prince Albert Victor - who died from flu in 1892. George V became king in 1910.
William and Kate's new baby will be a great-grandchild to the Queen and a great-great-great-great-great-grandchild of Queen Victoria.
Once he or she arrives, Prince Harry will shift down the line of succession to fifth in line to the throne, while the Duke of York will move to sixth place and princesses Beatrice and Eugenie to seventh and eighth.
The baby will be a prince or princess thanks to the Queen, who stepped in ahead of Prince George's birth to ensure all William's children would become HRHs with fitting titles.
The Queen issued a Letters Patent under the Great Seal of the Realm in December 2012 when Kate was just a few months' pregnant, declaring "all the children of the eldest son of the Prince of Wales should have and enjoy the style, title and attribute of royal highness with the titular dignity of prince or princess prefixed to their Christian names or with such other titles of honour".
A Letters Patent in 1917, issued by George V, limited titles within the royal family, meaning a daughter born to William or Kate would not have been an HRH but Lady (forename) Mountbatten-Windsor instead and a second-born son would also have lacked the HRH title and become Lord (forename) Mountbatten-Windsor rather than a prince.
William's cousin Princess Eugenie, who was born in 1990, was the last royal baby to be given the title Princess. The Earl and Countess of Wessex's daughter Lady Louise Mountbatten-Windsor is also technically a princess, but her parents decided, with the Queen's agreement, that she would use the courtesy title of the daughter of an Earl instead.
If the baby is a girl, it will be the first time a great granddaughter of a still-serving sovereign has been born in direct succession on the male line since 1897, when George VI's sister Princess Mary was born.
Belfast Telegraph Digital