William, also known as the Duke of Cambridge, is the grandson of the
"The Queen and members of both families are delighted with the news," read a statement from Buckingham Palace.
No due date for the baby was given, but the palace said the pregnancy has not passed the first trimester. The couple decided to announce the news because the Duchess of Cambridge, as Catherine is officially known, is experiencing acute morning sickness and had to cancel a appearance at an event in Oxford scheduled for Monday. Her attendance at future events is also in doubt.
"As with her first pregnancy, The Duchess is suffering from Hyperemesis gravidarum," the royal family's statement said. "The Duchess of Cambridge is being treated by doctors at Kensington Palace," the couple's official residence, it said.
British Prime Minister
Some British newspapers have already questioned what effect the announcement could have on Scotland's Sept. 18 referendum on independence. The pro-independence campaign is riding a growing wave of support in polls, suggesting that the outcome of the vote could be very close.
Scotland's pro-independence first minister, Alex Salmond, congratulated the couple on Twitter: "Wonderful to hear they're expecting their second baby -- very happy news!"
The online betting site Paddy Power is already offering novelty bets on the gender, hair color and name of the new baby. The names Elizabeth, William and Kate are among the contenders.