Prince Andrew looks glum on his weekly ride as brother Charles battles cancer – while Duke of York remains on the sidelines as other royals gather to fulfill King's public engagements

Prince Andrew looked somber during his weekly ride in his first public appearance since news broke that his brother King Charles is battling cancer.

The disgraced Duke of York appeared despondent as he trotted through a park wearing a navy blue jacket with the insignia of the Grenadier Guards.

He appeared to be gesticulating, accompanied by an accomplice, also on horseback, during their walk today.

Prince Andrew's older brother was revealed on Monday to have an unspecified form of cancer. Buckingham Palace said King Charles would halt royal engagements while he undergoes treatment.

Royal commentators have suggested that the departure of Prince Harry and Meghan Markle, and the disgrace of Prince Andrew, could leave the palace scrambling to find young royals who could take on royal responsibilities.

Prince Harry, 39, returned from the US this week to visit his father when news of the diagnosis broke. He arrived at the royal residence on Tuesday to spend “about 45 minutes” with his father.

The disgraced Duke of York appeared despondent during his weekly ride today

Andrew, who remains an outcast and is embroiled in a scandal over his alleged connection to pedophile financier Jeffrey Epstein, had not been seen since news of his brother's illness broke on Monday.

Other royals, including Princess Beatrice, were spotted early on Tuesday morning, with the princess leaving her residence at St James' Palace, next to her uncle's at Clarence House, before returning later in the day.

Princess Eugenie, Andrew's daughter, today published photos of her eldest son August on his third birthday, two days after she was spotted with Prince Harry's ex-girlfriend Cressida Bonas at a pub in Notting Hill.

And Prince Harry made a 24-hour visit to Britain on Wednesday to see his father before returning via Heathrow. The Duke of Sussex is said to have briefly met the King and Queen, but did not see his brother William or sister-in-law Kate Middleton.

It has not been confirmed what type of cancer the King has been diagnosed with, or what stage it is at, but it is believed it is not prostate cancer and was caught early.

Doctors noticed something was wrong when Charles, 75, was in hospital for surgery on a benign enlarged prostate, prompting further investigation.

Buckingham Palace reported that the king has since been diagnosed with cancer, only clarifying that it is not prostate cancer.

Palace officials say the type “receives expert care” on a regular, outpatient basis – but have not said what this entails.

As prince, Charles clashed with medical experts when speaking publicly in 2004 endorsed the idea that cancer patients could be treated with vitamin injections and fruit juices.

For now, the palace has confirmed that the king will not take part in most of his public duties, handing the job over to a skeleton staff of young royals.

It is not known how long King Charles will be forced to suspend public appearances, although it is believed he will continue to work on whatever tasks he can.

The King will still be busy with his red boxes of state business and official papers, as well as holding Privy Council meetings, which can be held via video, and weekly audiences with the Prime Minister, which can be held via telephone.

The palace has called for the king's privacy to be respected, especially during his treatment, but said he wanted to make his diagnosis public because of his long-standing support of cancer charities.

Buckingham Palace said in a statement on Monday: 'During The King's recent hospital procedure for a benign prostate enlargement, another area of ​​concern was noted. Subsequent diagnostic tests identified a form of cancer.”

Prince Harry arrives at Clarence House in London to meet his father

Prince Harry was escorted to Clarence House from London Heathrow after arriving from LAX

The statement continued: “His Majesty today commenced a schedule of regular treatments, during which time he has been advised by doctors to postpone public duties. During this period, His Majesty will continue to conduct state affairs and official paperwork as usual.

'The King is grateful to his medical team for their quick intervention, which was made possible thanks to his recent hospital procedure. He remains completely positive about his treatment and looks forward to returning to his full public role as soon as possible.

“His Majesty has chosen to share his diagnosis to avoid speculation and in the hope that it can increase public understanding for everyone around the world affected by cancer.”