An aide revealed tonight that the duchess is still suffering from hyperemesis gravidarum but said her condition is improving.
A slight baby bump could be seen beneath the Temperley dress worn by the Duchess, who is believed to be fewer than 12 weeks pregnant.
This is one of the causes that the Duchess of Cambridge puts her heart and soul into, which makes it all the more special that it will be the first event during her pregnancy with the third royal baby to be that she gets to attend.
William said: "It was Catherine who first realised that all three of us were working on mental health in our individual areas of focus". The statement came earlier than expected because Middleton had to miss out on events she is lined up to attend to take some rest.
The duke and duchess and Prince Harry arrived via a well-known hidden door in the Palace's white drawing room and waiting to meet them were leading figures from the mental health sector including Mind president and comic Stephen Fry.More news: Mark Zuckerberg's Weird VR Demo Tour of Devastated Puerto Rico
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WPA Pool via Getty Images Prince William speaks at a reception on World Mental Health Day to celebrate the impact of the Heads Together Charity at St James's Palace on October 10, 2017 in London, England. "Things that can't really be seen but that affect us every day, and talking about them can feel hard", she says, introducing a short animated film on the topic for children.
Normal morning sickness affects around 70 per cent of pregnant women, and causes some degree of vomiting and discomfort commonly during the first trimester of pregnancy.
We can't imagine what the Duchess of Cambridge has been going through as she's suffered from hyperemesis gravidarum, but we're happy to report that she looked happy and healthy at her first public appearance since it was announced she and Prince William are expecting their third child.
Those suffering from HG can be constantly sick morning, noon and night, and unable to keep any food or drink down. "All three of us have seen that mental health is at the heart of so numerous issues we are passionate about".