The Duke of Sussex will travel to the UK to visit King Charles "in the coming days" after Buckingham Palace announced the monarch had been diagnosed with cancer, the BBC understands.
A spokesperson for Prince Harry said he had spoken to his father about the diagnosis.
The duke moved to the US with his wife, Meghan, Duchess of Sussex, after they stepped back as senior royals in 2020.
Since then, his relationship with some other royals has been strained.
The spokesperson said Meghan would remain in the US with their two children.
The duke's last appearance at a Royal occasion took place in May, during the King's Coronation.
That was fleeting, with Prince Harry leaving immediately after the ceremony in Westminster Abbey.
The BBC understands that he was not invited to appear on the Buckingham Palace balcony following the ceremony.
A source also told US media outlet Page Six at the time that Prince Harry intended to make "every effort" to get back in time for his son, Archie's birthday - which was on the same day.
King Charles's cancer diagnosis
More recently the duke travelled to the UK to attend libel cases involving UK newspapers.
Prince Harry and Meghan have spoken out about life in the Royal Family and their disagreements with members of it in his memoir Spare, an interview with Oprah Winfrey and a Netflix documentary.
The prince told Winfrey that King Charles had stopped taking his calls when he was trying to discuss stepping down as a working royal.
Prince Harry also recalled that the King had pleaded with his sons, "Please, boys. Don't make my final years a misery" following the funeral of the King's father, Prince Philip.
But while they have had their differences, the King and prince have continued to have a relationship with the duke, calling his father on his 75th birthday last year.
The King called Prince Harry to tell him the news of his health, the palace said.
He also told the Prince of Wales, heir to the throne, as well as the King's siblings: the Princess Royal, Princess Anne; the Duke of York, Prince Andrew; and the Duke of Edinburgh, Prince Edward.