The royal, who has two children, Prince George, three, and Princess Charlotte, 22 months, made the comments during a speech at an event organised by Best Beginnings, a UK children's health charity on Thursday.

"Personally, becoming a mother has been such a rewarding and wonderful experience. However, at times it has also been a huge challenge," she said.

"Even for me, who has support at home that most mothers do not. Nothing can really prepare you for the sheer, overwhelming experience of what it means to become a mother. It's full of complex emotions of joy, exhaustion, love, and worry, all mixed together."

Since the birth of Prince George, the Duchess of Cambridge has been assisted by a home help team.

The family's current nanny, Maria Borrallo, joined the family when Prince George was eight months old. Dressed in a retro brown nurse's dress, Spanish-born Borrallo travels everywhere with the children.

(Oh, and the dress isn't just an aesthetic choice: it's the uniform for graduates of Norland College, a prestigious nannying school in Bath where nannies-to-be are trained in everything from nappy-changing to self-defence.)

"There is no rule book, no right or wrong; you just have to make it up and do the very best you can to care for your family," the Duchess continued.

"For many mothers, myself included, this can at times lead to a lack of confidence and feelings of ignorance. Sadly, for some mothers, this experience can be made so much harder due to challenges with our very mental health."

The candour is a rare move from the Duchess, who normally only divulges small tid bits about her private life in conversations with members of the public at charity events she attends (who subsequently tell the tabloids).

She went on to encourage women to seek assistance for their mental health during pregnancy and parenting in the same way as they would treat their physical health.

Along with her husband, Prince William, and his brother, Prince Harry, the Duchess is the founder of Heads Together, a mental health charity initiative that aims to reduce stigmatisation surrounding mental health diagnosis and dialogue. She was invited to speak at Thursday's event in a partnership between the two charities.