Prince William on Kate's pregnancy: "We are immensely thrilled"

Prince William said Monday that he and Kate, Duchess of Cambridge, are "thrilled" to be expecting their second child, but added that it's been "a tricky few days" for his pregnant wife.

The prince attended an official engagement in Oxford, England, solo because Kate is suffering from hyperemesis gravidarum -- the same extreme morning sickness that she had while pregnant with Prince George -- and could not attend. Kate, 32, is currently being treated by doctors at Kensington Palace, a spokesman said.

"It's been a tricky few days -- a week or so -- but obviously we're immensely thrilled, it's great news," William told reporters at the event.

"We're hoping things settle down and she feels a bit better," he added. "I'm going to look after her now."

The royal couple announced earlier that day that Kate was expecting royal baby No. 2. The new arrival will be fourth in line to Britain's throne and will make little George a big brother.

"Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting their second child," said a statement released Monday by Clarence House, the official residence of the Duke and Duchess.

"The Queen and members of both families are delighted with the news."