The Princess of Wales has marked her 44th birthday with a personal video on social media about the healing power of nature and the seasons.

"Even in the coldest, darkest season, winter has a way of bringing us stillness, patience and quiet consideration," said Catherine.

This is the concluding video in a four-part series, which has seen Catherine reflecting on the importance of nature to her, at a time when she has been recovering after cancer treatment.

"To be at one with nature, a quiet teacher and a soft voice that guides... Helping us to heal," she says, appearing wrapped up in a coat and hat in the winter scenes.

The video series, which began in the spring, has carried Catherine's personal and poetic thoughts on the positive impact of the natural world, over images of the changing seasons.

This latest video, issued by Kensington Palace and using images by filmmaker Will Warr, shows winter scenes around the UK, in woodlands, mountains and a murmuration of starlings over the sea.

"I find myself reflecting on how deeply grateful I am," says Catherine, who is shown walking in woods and putting her hand in a stream, in a video filmed in Berkshire, Cumbria, Gloucestershire, East Sussex and the Cotswolds.

In the wake of her recovery from cancer, the princess has spoken about the importance of kindness, calm and limiting the overuse of social media and mobile phones in a digital world.

She has also talked about nature's role in improving people's sense of wellbeing, both mentally and physically.

This sense of connection with nature has been framed in almost spiritual and mystical terms.

"For the rivers within us flow with ease, fears washed away, cleanse and purify. Come to peace with our tears and discover what it means to be alive," she says.

Catherine, in a social media post, described the video project on the seasons as a "deeply personal, creative reflection on how nature has helped me heal".

"But it is also a story about the power of nature and creativity in collective healing", she wrote.

"There is so much we can learn from mother nature, as we look to build a happier, healthier world."

On the theme of health, Catherine visited Charing Cross Hospital on Thursday, along with her husband Prince William, where they showed support for the efforts of NHS staff.

In a conversation with the volunteers, who were from Imperial Health Charity, Catherine spoke about how their work can sometimes go "unrecognised".

She said: "Sometimes the skills, the soft skills, the empathy and compassion, the kindness, goes beyond any job description.

"And it makes such a difference to patients and it often goes unrecognised."