However, on Tuesday, the 35-year-old powered through her illness in order to attend the reception at Buckingham Palace to commemorate World Mental Health Day. "She's delighted to be here tonight".
Although still reportedly dealing with severe morning sickness, Kate worked the event like a pro, greeting dignitaries while wearing a long dress by Temperley that showed a hint of a baby bump.
One of their initiatives that's close to the duchess' heart is Heads Together, a mental health campaign whose aim is to challenge mental health stigma and change how it is perceived.
Middleton had to endure the same complication during her previous pregnancies.
Kensington Palace shared a photo on Twitter of the trio at a reception "to celebrate those working in the mental health sector". But her health is most important and it's good to see that Middleton's condition is improving.
William, Kate and Harry have supported the mental health cause with their Heads Together campaign encouraging people to speak out about their psychological problems or be a sympathetic ear for others.
This is Princess Kate's first public appearance in six weeks.
Normal morning sickness affects about 70% of pregnant women and causes some degree of vomiting and discomfort normally in the first trimester (12 weeks) of pregnancy, but those suffering from hyperemesis gravidarum can be constantly sick throughout the day. "She had a very complicated period in the first few months", said a family member at the E!
Royal fans have not seen the Duchess since the end of August, when she joined the Duke of Cambridge and Prince Harry to mark the 20th anniversary of the death of Diana, Princess of Wales.
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