While it has historically been unusual for members of the Royal Family to talk about mental health, Middleton – along with husband Prince William and brother-in-law Prince Harry – has chosen it as one of her key causes.

In January, the royals criticised the traditional British mentality of “keep quiet and carry on” as they launched their Heads Together campaign.

“There are times when, whoever we are, it is hard to cope with challenges – and when that happens being open and honest and asking for help is life-changing,” said William, the Duke of Cambridge.

He added: “It is no exaggeration to say that conversations – simple conversations – can be life-changing: in a workplace, in your kitchen at home, with a friend, family member or colleague.

“And that’s what Catherine, Harry and I want to do – we want more people to be having those conversations.”

Images: Rex Features

Kate Middleton opens up about motherhood and mental illness