She had been admitted to London's King Edward VII Hospital suffering from hyperemesis gravidarum - an acute form of morning sickness - on Monday, prompting the early announcement of her pregnancy.
[The couple leave hospital today]
St James's Palace has confirmed that Kate will now stay at Kensington Palace for a period of rest.
Her husband Prince William had visited her on Tuesday and was later photographed leaving the hospital.
The Duchess remained in hospital until this morning as she continued to receive treatment and hydration for condition.
A nurse at the hospital was tricked by an Australian radio show into giving out minor details of Kate's condition. The royal couple were later said to be "furious" about the prank.
The pair's child will be third in line to the throne, and is also in direct succession to the crown.
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