Kate Middleton represents Fab Four on London outing – see all the photos

The Duchess of Cambridge has been flying the flag for mental health for years, and on Thursday, Kate attended a very important event in London. As one of the four patrons of The Royal Foundation, Kate was a guest of honour at the Mental Health in Education conference at Mercers' Hall. The event focused on children's mental health, with head teachers and other education experts discussing what more can be done to tackle mental health issues in schools.

Kate, who is a firm believer in early intervention to prevent problems later on in children's lives, looked typically elegant on her day out. The mum-of-three went business chic in a tweed blazer and skirt combo. She was given a warm welcome at the conference, with a number of royal fans waiting outside Mercers' Hall to catch a glimpse of Prince William's wife.

Let's take a look at the best photos from Kate's day out…

Kate arrived just after 11am, looking ready to immerse herself in the conference. Prince George, Princess Charlotte and Prince Louis' mum wore a navy and black tweed suit and kept warm with thick black tights.

She was given a warm welcome at the conference.

A closer look at Kate's flawless makeup look and her £3,000 18ct white gold and diamond earrings by Kiki McDonough.

The royal was reunited with broadcaster and presenter Kate Silverton, who was hosting the conference.

Through her work with The Royal Foundation, Kate's focus has always been on supporting and promoting the mental health of children and young people.

The event brought together delegates from across the mental health and education sectors to explore and discuss the benefits of collaborative working and what more can be done to tackle mental health issues in schools.

The conference saw a full day of speakers, panel discussions and breakout sessions. Kate sat in on a number of sessions, including one on how mental health modules can be integrated into teacher training courses, and another on the role of school leaders in creating a culture of wellbeing in schools.

Kate also met head teachers from schools who are currently piloting The Royal Foundation's Mentally Healthy Schools programme. Kate launched the Mentally Healthy Schools website last year, which gives free access to mental health resources.