Kate Middleton has made her first public appearance since news broke of her third pregnancy, attending a Buckingham Palace reception marking World Mental Health Day.

The Duchess of Cambridge, who has been suffering from hyperemesis gravidarum – a severe form of morning sickness – had not attended an official engagement for more than a month and even missed Prince George’s first day at school at the start of September.

Wearing a long, grey dress Temperley dress, a visibly pregnant Kate looked on as her husband Prince William and brother-in-law Prince Harry made speeches recognising the contribution of mental health workers.

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.

Pregnant Kate makes her first appearance in a dress by Temperley pic.twitter.com/73gsvEHPmm

— Victoria Murphy (@byQueenVic) October 10, 2017

Kate made an unusual appearance without William by her side in a  video released last month aimed at educating young children about mental health.

Kensington Palace announced on September 4 that Kate was expecting her third child and, like previous pregnancies with Prince George and Princess Charlotte, was suffering from severe morning sickness.

Vanity Fair quoted a palace aide as saying: “The Duchess’s condition is improving but she is still suffering from hyperemesis gravidarum.”

The Duchess is thought to be less than 12 weeks’ pregnant with her bout of hyperemesis gravidarum  forcing her to pull out of an event at the beginning of September, which prompted the palace to make the pregnancy announcement early.

Kate’s previous public appearance was on was August 30, when she toured the Princess Diana garden at Kensington Palace with William in advance of the 20th anniversary of Diana’s death.

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.

– With agencies