The Duchess of Cambridge has written a touching tribute to midwives following a secret visit to a London hospital.

Duchess of Cambridge

Duchess of Cambridge

The 37-year-old royal - who has kids Prince George, six, Princess Charlotte, four, and 20-month-old Prince Louis - thanked the midwives for showing her their work at a maternity unit in London in November.

In an open letter, the Duchess wrote: "Your work often goes on behind the scenes, and away from the spotlight. Recently however, I was privileged enough to witness a small section of it first hand, spending several days at Kingston Hospital's maternity unit.

"Although this was not my first encounter with the care and kindness provided by midwives across the country, it gave me a broader insight into the true impact you have on everybody you help."

The Duchess' letter - which was published ahead of the World Health Organization's international Year of the Nurse and Midwife in 2020 - also praised the selflessness of midwives across the country.

She said: "The founder of modern nursing, Florence Nightingale - whose 200th anniversary we celebrate next year - once said, 'I attribute my success to this: I never have or took an excuse' and it is that mantra that I have seen time and time again in all of my encounters with you.

"You don't ask for praise or for recognition but instead unwaveringly continue your amazing work bringing new life into our world.

"You continue to demonstrate that despite your technical mastery and the advancement of modern medicine, it is the human to human relationships and simple acts of kindness that sometimes mean the most."

Professor Jacqueline Dunkley-Bent, England's chief midwifery officer, has already described the Duchess' praise as a "huge honour".

She added: "As we look ahead to 2020, her support will no doubt be a massive boost for all those working in maternity services as we celebrate the year of the nurse and the midwife."