Prince Andrew goes for a ride a day after it was announced King Charles will be returning to public duties as monarch continues cancer treatment

Prince Andrew was spotted in deep thought on a horse ride around the Windsor Castle estate, just a day after his elder brother, King Charles III, announced he will return to public-facing duties for the first time since being diagnosed with cancer.

The Duke of York, 64, looked contemplative alongside his female riding companion as he travelled around the Berkshire estate on his usual Saturday morning ride.

Andrew was dressed in a khaki jacket, grey jumper, black trousers and a black and white striped helmet for the excursion.

His riding companion flashed a smile after noticing the presence of a photographer as they enjoyed a slow-paced ride through the leafy grounds, before heading back towards Windsor castle.

Andrew was spotted earlier driving in his dark-coloured Range Rover to the castle, which next week will play host to the annual Royal Windsor Horse Show.

Prince Andrew was spotted in deep thought on a horse ride around the Windsor Castle estate, just a day after his elder brother, King Charles III , announced he will return to public-facing duties for the first time since being diagnosed with cancer 

The Duke of York, 64, looked contemplative alongside his female riding companion as he travelled around the Berkshire estate on his usual Saturday morning ride

Several members of the Royal Family are expected to make an appearance at the event, which runs from 1 to 5 May.

Prince Andrew's latest appearance comes just a day after Buckingham Palace released a statement announcing that King Charles III will return to public duties next week. 

His Majesty is not yet clear of the disease and is still undergoing treatment, but his medical team are understood to be 'pleased with the progress made so far' and 'remain positive' about his recovery.

After his cancer diagnosis was announced on February 6, the King postponed all public-facing engagement but continued with his duties as head of state behind palace walls, conducting audiences and Privy Council meetings. 

On Tuesday, the King - who is patron of Macmillan Cancer Support - will make his first public appearance in weeks alongside the Queen on a visit to an undisclosed cancer treatment centre.

It is a deeply poignant engagement given his own cancer battle as well as that of his daughter-in-law, the Princess of Wales and they are expected to meet medical specialists and patients. 

The royal event aims to raise awareness of the importance of early diagnosis and highlight innovative research, supported by Cancer Research UK, taking place at the hospital.

Andrew was spotted earlier driving in his dark-coloured Range Rover to the castle, which next week will play host to the annual Royal Windsor Horse Show

The King's brother was seen just days before the start of the Royal Windsor Horse Show, where several members of the Royal Family are expected to make an appearance

There are also plans to host an incoming state visit by The Emperor and Empress of Japan in late June at the request of the government.

In a statement Buckingham Palace said on Friday night: 'His Majesty The King will shortly return to public-facing duties after a period of treatment and recuperation following his recent cancer diagnosis.

'To help mark this milestone, The King and Queen will make a joint visit to a cancer treatment centre next Tuesday, where they will meet medical specialists and patients. 

'This visit will be the first in a number of external engagements His Majesty will undertake in the weeks ahead. 

'In addition, The King and Queen will host Their Majesties The Emperor and Empress of Japan for a State Visit in June, at the request of HM Government.

'As the first anniversary of The Coronation approaches, Their Majesties remain deeply grateful for the many kindnesses and good wishes they have received from around the world throughout the joys and challenges of the past year.'

King Charles III looked well in a recently-released photograph of himself with Queen Camilla, taken by portrait photographer Millie Pilkington, in Buckingham Palace Gardens on April 10, the day after their 19th wedding anniversary. The image was released to mark the first anniversary of their Coronation

 The Mail understands that the King is also hopeful of undertaking investitures - the handing out of honours to worthy members of the public - in the coming weeks and months.

Again, it is likely that the ceremonies will be adjusted to take account of his condition and ongoing treatment - perhaps with smaller numbers of recipients.

Buckingham Palace declined to comment on whether members of the wider Royal Family, including Harry and Meghan, were informed of his news in advance.

Charles has been receiving care as an outpatient since early February, and the announcement will be a boost for the monarchy coming to terms with King and the Princess of Wales as cancer patients. 

Buckingham Palace has not revealed the nature of the monarch's cancer or details of the treatment he has received.

The Daily Mail has already exclusively revealed that planning is already underway for him to attend his official birthday celebrations, Trooping the Colour, as well as Royal Ascot and the summer garden parties. 

It is unclear yet whether he will be able to travel to Normandy in June for the major D-Day anniversary commemorations or to Australia, New Zealand and Samoa as planned in October, but it is understood that the King is keen to if his health allows.

A spokesman added today: ' Planning continues for ways in which Their Majesties may attend such Summer and Autumn engagements, though nothing can be confirmed or guaranteed at this stage. 

'All future plans remain subject to doctors' advice nearer the time, with appropriate adaptations made where necessary to minimise any risks to His Majesty's continued recovery.' 

His Majesty is not yet clear of the disease and is still undergoing treatment, but his medical team are understood to be 'pleased with the progress made so far'. Pictured: King Charles III and Queen Camilla leave The London Clinic in January after he received treatment for an enlarged prostate. He would later reveal he had been given a cancer diagnosis following the procedure