The Duke and Duchess Of Cambridge And Prince Harry Support World Mental Health Day at Buckingham Palace on 10, October 2017 in London, England

(L-R) Prince William, Duke of Cambridge, Catherine, Duchess of Cambridge and Prince Harry hosted the reception to celebrate those who work to improve the nation's mental health in central London on October 10, 2017

The pregnant Cathrine, Duchess of Cambridge spent time greeting guests in one of the opulent reception rooms

The Duchess of Cambridge beamed as she, Prince William on right and Prince Harry left the reception

Prince Harry, who recently returned from Toronto, looked relaxed as he mingled with groups of guests

Prince William, Duke of Cambridge delivered a speech during a reception at Buckingham Palace to celebrate World Mental Health Day in central London on October 10, 2017

(L-R) Prince William, Duke of Cambridge with Catherine, Duchess of Cambridge and Prince Harry attend a reception on World Mental Health Day to celebrate the contribution of those working in the mental health sector across the UK at Buckingham Palace on October 10, 2017 in London, England.

Catherine, Duchess of Cambridge look ladylike in a pretty blue hue Temperley London eclipse lace collar dress as she joined her husband Prince William, Duke of Cambridge, host a Buckingham Palace reception for mental health workers.

Prince William, left, the Duchess of Cambridge and Prince Harry came together to co-host the reception at Buckingham Palace for the World Mental Health day on October 10, 2017.

Prince William, Duke of Cambridge was by Catherine, Duchess of Cambridge's side as she spent time speaking to guests at the Buckingham Palace reception

Prince Harry, pictured, has spoken out about his own struggles with his mental health in the past, as he attends the World Mental Health day reception at Buckingham Palace.

Catherine, Duchess of Cambridge, who looked relaxed at the glamorous event, mingled with guests at Buckingham Palace

Catherine, Duchess of Cambridge looked radiant in a £795 powder blue lace dress by Temperley London which skimmed over her bump. She paired with black suede heels and a small black clutch bag. She also sported £3,500 Kiki McDonough blue topaz and diamond earrings, as she attends the World Mental Health day reception at Buckingham Palace.

Prince William, Duke of Cambridge accompanied his wife Catherine, Duchess of Cambridge (center), who beamed as she spoke to a guest at the reception at Buckingham Palace

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge who are expecting their third child together, shared a light-hearted moment during the reception for the World Mental Health Day at Buckingham Palace on 10, October 2017 in London, England.

The Duchess of Cambridge, who is still suffering from morning sickness, looked animated as she spoke to guests at Buckingham Palace for the World Mental Health day reception.

Catherine, Duchess of Cambridge, looked animated as she spoke to guests at the event despite still feeling unwell during the World Mental Health day reception at Buckingham Palace

Catherine, Duchess of Cambridge looked radiant in a £795 powder blue lace dress by Temperley London which revealed a small baby bump as she made her first appearance since announcing her pregnancy to host royal reception at Buckingham Palace for the World Mental Health day.

Catherine, Duchess of Cambridge opted for a £795 powder blue dress by Temperley London lace design with flared cuffs and pretty pleats which are spliced with cotton panels, a velvet ties and button details in contrasting black, as she made her first appearance since announcing her pregnancy last month to host royal reception at Buckingham Palace for the World Mental Health day.

The elegant Duchess of Cambridge accessorized her feminine frock with a pair of black suede heels and a small clutch bag, as she attends the World Mental Health Day at Buckingham Palace on 10, October 2017 in London, England.

Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge support World Mental Health Day at Buckingham Palace on 10, October 2017 in London, England.

Catherine, Duchess of Cambridge attends a reception on World Mental Health Day to celebrate the contribution of those working in the mental health sector across the UK at Buckingham Palace on October 10, 2017 in London, England.

Britain's Catherine, Duchess of Cambridge attends a reception at Buckingham Palace to celebrate World Mental Health Day in central London on October 10, 2017

Catherine, Duchess of Cambridge revealed a small baby bump as she made her first appearance since announcing her pregnancy last month, seen speaking to guests at the Buckingham Palace reception.

Prince William, Duke of Cambridge with Catherine, Duchess of Cambridge and Harry hosted the event to highlight the tireless work of mental health workers at Buckingham Palace

Catherine, Duchess of Cambridge looks elegant in pretty blue hue Temperley London eclipse lace collar dress with flared cuffs and pretty pleats which are spliced with cotton panels. She accessorized her feminine frock with a pair of black suede heels and a small clutch bag. Making a statement with her jewelry, sported £3,500 Kiki McDonough blue topaz and diamond earrings, as she co-host a glittering Buckingham Palace reception to mark World Mental Health Day.

Prince William, Duke of Cambridge 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.

Prince Harry 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.

Catherine, Duchess of Cambridge and Prince Harry attend a reception on World Mental Health Day to celebrate the contribution of those working in the mental health sector across the UK at Buckingham Palace on October 10, 2017 in London, England.

Catherine, Duchess of Cambridge looked radiant in a £795 powder blue lace dress by Temperley London which skimmed over her bump, attends a glittering Buckingham Palace reception to mark World Mental Health Day.

Prince William, Duke of Cambridge attends a reception on World Mental Health Day to celebrate the contribution of those working in the mental health sector across the UK at Buckingham Palace on October 10, 2017 in London, England.

(L-R) Prince William, Duke of Cambridge with wife Catherine, Duchess of Cambridge and his younger brother Prince Harry attend a reception on World Mental Health Day to celebrate the contribution of those working in the mental health sector across the UK at Buckingham Palace on October 10, 2017 in London, England.

Prince William, left, Catherine, Duchess of Cambridge and Prince Harry came together to co-host the reception at Buckingham Palace for the World Mental Health day.

Catherine, Duchess of Cambridge opted a powder blue lace dress by Temperley London, appeared for the first time since breaking the news of her third child, appearing at Buckingham Palace for the World Mental Health day reception.

Catherine, Duchess of Cambridge looks elegant in a pretty blue hue Temperley London eclipse lace collar dress with flared cuffs and pretty pleats which are spliced with cotton panels, with the velvet ties and button details in contrasting black. She paired with a black suede heels and a small clutch bag, to co-host the reception at Buckingham Palace for the World Mental Health day.