It's been a week of unprecedented revelations from the royal family, with Prince Harry admitting he'd come close to a 'breakdown' over his mother's death, and today Kate followed in her brother-in-law's footsteps by revealing her own struggles with coming to terms with motherhood.
After hearing from two mothers who admitted feeling in need of a friend when they had small babies, she also said of being a mum: 'It is lonely at times. You do feel quite isolated.
'But actually so many other mothers are going through exactly what you're going through. But it's being brave enough, like you obviously were, to reach out.'
She was speaking to Katie Massie-Taylor and Sarah Hesz, the co-founders of an app called Mush aimed at connecting new mothers, and supporters of charity Heads Together.
The Duchess, along with her husband the Duke and Prince Harry, was appearing at the new Global Academy, a new west London school which builds mental health wellbeing classes into its curriculum.
She also made a candid revelation about her lack of confidence as she chatted to Oliver Monger, 16, from Uxbridge, who joined the academy when it opened last September, and hopes to go into the film industry.
He told the Duchess: 'I've not really had a problem I've needed to talk to someone about, but meeting you is a new thing. I don't really know how to speak to someone so high. I'm quite shy.'
Smiling, Kate interjected: 'I'm shy as well, so don't worry.'
Afterwards an exhilarated Oliver said: 'That was just fantastic. It has really boosted my confidence. I had no idea what to say at first but she really put me at ease.'
The visit follows five days of intense campaigning by the young royals on the issue, with Prince Harry speaking of his own therapy, and the Duke of Cambridge disclosing he still feels the shock of their mother's death.
The Duchess, who had been hearing how students benefitted from their classes, said: 'It's having those age-appropriate conversations and bringing in the topic of mental health really at different levels. Whether it be at a happy level or a more serious level.
'It's the same with younger children, and even helping parents to start these conversations from a much earlier age but through play even if their language hasn't yet developed. 'Very young children actually don't even have the language to express how they're feeling, so it comes out in behavioural problems.
'So being able to find ways to address those problems really early on is great.'
Prince Harry told students that, in the past, discussing mental health had been seen as a 'dry, depressing subject' which 'turned people away'.
'If you can bring a light-hearted humour and encourage people to speak about the subject in that way, it puts a smile on your face,' he said.
The Duke of Cambridge said: 'The strongest guys are the ones who can talk about it.
'The weak guys are the ones who bottle it away and it makes their lives spiral completely out of control. And it ruins their lives eventually.
'You waste a lot of your life worrying and stressing about stuff that frankly, if you have a conversation and talk to somebody it will make everything much better.'
Prince Harry said: 'I think the whole country has shown a real appetite to want to talk about this.
'We've sort of unlocked something. It's like taking the lid off a boiling pan. It's been simmering for a very long time and everyone's desperate for it to come out. 'It's just providing a mechanism. We need to prioritise mental health.'
Kate was at the academy this morning with Princes William and Harry to officially open the premises in support of their mental health initiative Heads Together.
During their visit the three met students training to be the next generation of production staff, and visited the breakfast shows of flagship Global radio stations LBC, Heart and Capital being broadcast from the school.