The announcement on Monday that the Duke and Duchess of Cambridge, as William and Kate are officially known, was greeted with enthusiasm in Britain.

Congratulations poured in, and one of the first to congratulate the couple was British Prime Minister David Cameron.

"I'm delighted by the news that the Duke and Duchess of Cambridge are expecting a baby," Cameron posted on Twitter. "They will make wonderful parents. The whole nation will be celebrating with them tonight."

The palace announced on Monday that Kate had been admitted to a London hospital after suffering from acute morning sickness. She will likely stay in the hospital for a few days, and then begin a "period of rest," the palace said.

Planned legislation in Britain means that William and Kate's child will automatically become third in the line of succession to the British throne regardless of the baby's gender. The new law would end the practice of a first-born daughter losing her place to a son born later.

Prince Charles is the current heir to the throne of Queen Elizabeth. William would come next, and his child would replace his brother, Prince Harry, in third.

The palace did not release any details regarding a due date of the royal baby, but observers speculate Kate is less than 12 weeks pregnant, which would mean a due date of sometime in the summer.

mz/jm (Reuters, AFP, dpa)