Vanity Fair quoted a palace aide as saying: "The Duchess's condition is improving but she is still suffering from hyperemesis gravidarum". In the first few months, the Duchess had to retire from her royal functions because she was too ill to be able to fulfill her commitments.
Dr Nicola Byrom, founder of the mental health charity Student Minds, said after chatting to Kate: "She's fantastic, what a fighter that she's here, that she's putting other people above herself".
The Duchess of Cambridge attended a reception at Buckingham Palace this evening to mark World Mental Health Day, marking her first public appearance since the news of her third pregnancy was announced.
The palace has not announced when the baby is due but it is believed Kate is less than 12 weeks pregnant.
The Duke and Duchess and Prince Harry met leading figures in the mental health sector at the reception, including Mind president and comic Stephen Fry.
"She had seen that at the core of adult issues like addiction and family breakdown, unresolved childhood mental health issues were often part of the problem".
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.
"Harry had seen that it wasn't enough to help veterans recover from their physical injuries without acknowledging the emotional and mental support they required".
She's been battling severe morning sickness.
Kate' last public engagement was on August 30th when she accompanied her husband and brother-in-law to the Princess Diana memorial garden.
Hyperemesis gravidarum can cause severe nausea and vomiting and requires supplementary hydration and nutrients.
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.