But she emphasised: “Doing what I can to stay cancer-free is now my focus.”

The video, shot in Norfolk in August, shows the Wales family as they have never been seen by the public before.

The Prince and Princess are filmed kissing, her head resting on his shoulder, and enveloping Prince George, Princess Charlotte and Prince Louis in hugs.

Catherine is seen walking through corn fields, driving, playing cards with her parents, Carole and Michael Middleton, helping the children climb trees and scramble up haybales.

In one intimate shot, the family are seen lying on a Norfolk beach, embracing.

It is intended to illustrate the Princess’s message that she has renewed gratitude for her “simple yet important things in life”, “of simply loving and being loved”.

The princess is expected to attend a handful of public engagements before the end of the year, subject to changes in her health.

They are likely to include appearing at the Cenotaph on Remembrance Sunday and hosting her annual Westminster Abbey carol concert for children. She will also hold a “small number” of meetings, some of which will appear in the Court Circular.

In March, the princess released a video message telling the world that, following major abdominal surgery in January “tests after the operation found cancer had been present” and that her “medical team therefore advised that I should undergo a course of preventative chemotherapy”.

In her second video message, released on Monday, she said: “Doing what I can to stay cancer-free is now my focus.”

The footage was filmed by Will Warr, who has previously produced videos of the princess and her children visiting a baby bank, and of the family preparing for the Coronation.

It includes what appears to be self-shot footage, with George saying “is this on?” as he fiddles with a camera, and his siblings shouting “hello!”

The princess, who finishes the video by watching a butterfly land on her hands and fly away again, says: “As the summer comes to an end, I cannot tell you what a relief it is to have finally completed my chemotherapy treatment.

“The last nine months have been incredibly tough for us as a family. Life as you know it can change in an instant, and we have had to find a way to navigate the stormy waters and road unknown.

“The cancer journey is complex, scary and unpredictable for everyone, especially those closest to you. With humility, it also brings you face-to-face with your own vulnerabilities in a way you have never considered before, and with that, a new perspective on everything.

“This time has above all reminded William and me to reflect and be grateful for the simple yet important things in life, which so many of us often take for granted. Of simply loving and being loved.

“Doing what I can to stay cancer-free is now my focus. Although I have finished chemotherapy, my path to healing and full recovery is long, and I must continue to take each day as it comes.

“I am, however, looking forward to being back at work and undertaking a few more public engagements in the coming months when I can.

“Despite all that has gone before, I enter this new phase of recovery with a renewed sense of hope and appreciation of life.”

In a direct message to the public, she added: “William and I are so grateful for the support we have received, and have drawn great strength from all those who are helping us at this time. Everyone’s kindness, empathy and compassion has been truly humbling.

“To all those who are continuing their own cancer journey – I remain with you, side by side, hand in hand. Out of darknes, can come light, so let that light shine bright.”

The video was released by Kensington Palace as the Wales family return to work and school following their summer holidays.

They have spent the summer out of the spotlight, enjoying time at their home in Norfolk as well as their annual trip to join the royal family at Balmoral.

The princess was photographed on August 25 on her way to church at Balmoral, driven by William and looking well. She was also spotted with her husband and three children at a family festival in Norfolk this summer, where they are said to have abseiled and played Nerf gun wars.

Kensington Palace last updated the public on the princess’ condition in June, when it issued a written statement saying she was making “good progress” in her chemotherapy but was “not out of the woods yet”.

The princess said she was having “good days and bad days”, and learning to be “patient” in allowing herself to heal.

The following day, on June 15, she joined William, George, Charlotte and Louis for Trooping the Colour, the King’s birthday parade, riding in a carriage before appearing with the full working family on the Buckingham Palace balcony.

In July, she attended the men’s final of Wimbledon, where she received a standing ovation to welcome her and her daughter to their seats.

The princess had major abdominal surgery in January, spending nearly two weeks in hospital for an undisclosed condition. In March, she released a personal video telling the world she was having treatment following the discovery of cancer.

At the time of the update, on March 22, the Palace said the princess would return to official duties only when she is “cleared to do so by her medical team”.