To mark World Mental Health Day, The Duke and Duchess of Cambridge and Prince Harry are hosting a reception at Buckingham Palace in honour of those who work in the U.K. mental health sector.

One of the guests, Dame Esther Rantzen, said, "We are seeing with Childline more and more contact both online and over the phone from young people suffering with mental health issues such as depression, anxiety and eating disorders. It can be a very stigmatising issue. Similarly with older people, this is a significant issue. And many have needed encouragement to talk."

Earlier William, Kate and Harry attended another reception to thank those who played a big role in the success of the Heads Together campaign.

In May 2016, Their Royal Highnesses set out to change the way we speak about our mental health though Heads Together, a mental health campaign led by The Royal Foundation in partnership with YoungMinds and seven other charities. It aims to challenge mental health stigma and change how it is perceived.

In the lead up to World Mental Health Day, The Duke of Cambridge paid a visit to Data Observatory at Imperial College London to receive a briefing on the progress the Heads Together campaign and its partners have made towards the national conversation on mental health. With 14,000 people surveyed, this was the largest ever survey on British mental health. It found that the public’s perception of mental health changed when the Heads Together initiative was in full swing earlier this year. In February, 45% of men and 52% of women said they talked about their own mental health. By May, 60% of men and 61% of women had such discussions. It was actually the Duchess who came up with the genesis of Heads Together, after realizing that she, William and Harry were working on mental health in their own individual areas — William with men, Harry with the military, and Kate with children, young people and mothers. This marks the Duchess's first engagement since the announcement that she is having a third child. She is still suffering from hyperemesis gravidarum, but her condition is improving.

For her first appearance since announcing her third pregnancy, the Duchess opted for a new dress by Temperley London. As she quite frequently does, Kate added a subtle nod to the event itself through her clothing by opting for a blue dress — blue being the colour of mental health awareness.

Temperley's 'Eclipse Lace Collar Dress' is available for £665 and comes in iris (Kate's colour), black and white. The midi dress is inspired by Elizabethan and Baroque portraits of ladies wearing high necklines and ruffles. It is made from corded lace and has black velvet trims and a pleated skirt spliced with cotton-voile panels.

It is described: "A modern take on the lace dress underpinned by the season's Elizabethan influence, the Eclipse Lace Collar Dress is shaped into a sleek A-line silhouette. Cut from contemporary corded lace, this elegant iris-hued dress is finished with scalloped edges, frilled sleeves and neckline, and a contrast velvet neck tie."

This style of dress has been favoured by the Duchess over the last couple of years. The midi length, the lace overlay and the high, Elizabethan-inspired neckline are all features we often see her wearing. You can see some similar dresses — the most similar being the green Temperley dress worn in India last year.

Kate carried her Mulberry Bayswater clutch and wore her trusty Gianvito Rossi black suede pumps that are available for £470 at Net-A-Porter.

She also wore her Kiki McDonough 'Blue Topaz & Diamond Drop Earrings in White Gold' which are available for £2916.67.