Britain's Prince William leaves the King Edward VII hospital with his wife Catherine, Duchess of Cambridge, London December 6, 2012. Prince William's pregnant wife Kate left the King Edward VII hospital in central London on Thursday where she had spent four days being treated for acute morning sickness. [Photo/Agencies]

The Duchess of Cambridge left a London hospital Thursday after being treated for acute morning sickness related to her pregnancy.

Related: UK's Prince William and wife Kate expecting a baby

Clutching a small bouquet of yellow roses, the former Kate Middleton smiled and posed briefly for a photograph alongside her husband, Prince William, before leaving King Edward VII Hospital. She stepped delicately into a waiting car.

The couple's office said she would head to Kensington Palace in London for a period of rest. She had been in the hospital since Monday. Officials from St. James's Palace have said the duchess is not yet 12 weeks pregnant with the couple's first child.

William visited his wife at the hospital every day, while media from around the world camped outside, seeking any news on the royal pregnancy.

Royal officials announced Monday that the Duchess was pregnant, their hand forced by her admission into the hospital.

But the stay of one of the world's most recognized women was complicated by a breach of her privacy.

Two Australian radio disc jockeys impersonating Queen Elizabeth II and Prince Charles placed a prank call to the hospital early Tuesday, and persuaded an unwitting nurse to tell them all about the Duchess' condition.

Photos: Prince William and wife Kate expecting a baby