Princess Anne, 73, is expected to make a full recovery after receiving a head injury. Photo: Jonathan Brady / POOL / AFP)
By Sean Coughlan, BBC royal correspondent
The Princess Royal has been admitted to hospital with a minor head injury and concussion thought to be caused by a horse.
Princess Anne, 73, is expected to make a full and swift recovery after an incident at her Gatcombe Park estate in Gloucestershire on Sunday, said Buckingham Palace, adding that she is "recovering well" and is "in a comfortable condition".
Sources suggest her injury is consistent with an impact from a horse's head or legs.
"The King has been kept closely informed and joins the whole Royal Family in sending his fondest love and well-wishes to the Princess for a speedy recovery," the palace statement added.
Princess Anne's trip to Canada that was due to begin at the end of this week has been postponed. She will also miss the state banquet for the Japanese state visit on Tuesday.
The Princess Royal was injured on Sunday evening when she was out walking on her estate and horses were nearby.
The cause of the head wound is unconfirmed, with the lack of certainty reflecting that the princess suffered from concussion in the incident.
Emergency services were called to the estate and the princess was taken to Southmead Hospital, Bristol.
The princess is conscious and is expected to stay in hospital until later this week "as a precautionary measure for observation", a Buckingham Palace statement said.
Southmead is an NHS hospital, part of the North Bristol NHS Trust, and has a number of major specialities, including neuroscience.
Her husband Admiral Sir Tim Laurence and her daughter Zara and son Peter were on the estate at the time. Her husband then travelled with her to hospital.
In a statement, Buckingham Palace said: "The Princess Royal has sustained minor injuries and concussion following an incident on the Gatcombe Park estate yesterday evening."
According to the NHS, concussion can be the result of a "temporary injury to the brain caused by a bump, blow or jolt".
It can cause forgetfulness, tiredness and a lack of concentration and can take a couple of weeks before a full recovery.
The hospitalisation of Princess Anne is the latest health problem facing the Royal Family.
King Charles and the Princess of Wales both have had a cancer diagnosis this year, limiting their public engagements.
Princess Anne, known as one of the most hard-working royals, continued to help in their absence with numerous engagements, supporting the depleted royal ranks.
This week she had a series of events planned, including the Japanese state visit, with other engagements scheduled in Scotland, Hampshire and Gloucestershire.
Her sense of public duty combined with a no-nonsense approach has helped her status as one of the most popular royals, with consistently high approval ratings in opinion polls.
She is known for her interest in horses and her achievements in equestrian sports, becoming the first member of the Royal Family to compete in the Olympics, in the games in Montreal in 1976.
As the second child of Elizabeth II and Prince Philip she was third in line to the throne when she was born and she is now 17th in the line of succession.
She has married twice. Her first husband, Captain Mark Phillips, is the father of her two children, Peter and Zara.
- BBC