Harry arrived from Los Angeles on Tuesday afternoon to London's Heathrow Airport, and from there he drove to Clarence House, the royal couple's residence.
Buckingham Palace – the royal family's office in London – announced the night before that its doctors had diagnosed the king with cancer when he was being treated for an enlarged prostate at the end of January.
According to information, this is not prostate cancer, but the palace did not mention which organ was attacked by the disease in Karolyi.
According to press reports on Tuesday citing court officials, the king called Harry personally when he was told of the diagnosis, and the prince immediately boarded the plane.
Harry – who is fifth in line to the British throne – gave up his job as a senior member of the royal family four years ago and moved to California with his American wife, Princess Meghan.
Since then, the Duke of Sussex's relationship with the rest of the family has become strained, led by his brother William, the heir to the throne.
What made the situation worse was the book that Harry published last year, in which he revealed sensitive details about the life of the royal family.
Harry attended Charles' coronation at Westminster Abbey in London last May, but did not visit the house on the occasion of his father's 75th birthday, which was on November 14.
The King will continue to perform his duties as head of state and obtain the necessary official government papers during his treatment for cancer, but his doctors recommended postponing his public programs for the duration of his treatment.
On Tuesday, the King's sister, Princess Anne, presented the medals on behalf of Charles at Windsor Castle on the western border of London, and he then traveled to central England, where he will participate in public events that were originally official for the King.
According to court officials, Karolyi's eldest son, heir to the throne Vilmos, will also begin work again starting Wednesday.
The Prince of Wales has withdrawn from public appearances in recent weeks after his wife, Princess Catherine – for reasons not determined by the court – underwent abdominal surgery at the London Clinic, a private hospital in London, the same place where the King is being treated..
Katalin, who spent almost two weeks in hospital, is currently recovering at home and, according to the court, is unlikely to return to her public duties before Easter.
The cover image is an illustration. Image source: Patrick van Cutwijk/Getty Images