Soon after King Charles III went public with his cancer diagnosis, his estranged son Prince Harry arrived to be by his side in the United Kingdom.

A source in the United Kingdom told Fox News Digital that Prince Harry had arrived on Tuesday, and was seen entering Clarence House, the London residence of the King.

A car believed to be transporting the Prince was spotted at Heathrow Airport.

KING CHARLES' CANCER DIAGNOSIS LEAVES ROYAL FAMILY ‘VERY THIN ON THE GROUND': EXPERT

Prince Harry arrives in Clarence House and seen looking away from camera

Prince Harry met his ailing father at his London residence, Clarence House. (News Licensing / MEGA)

Prince Harry's side profile in a car as he arrives at Clarence House in London

Prince Harry is photographed arriving to Clarence House after landing at Heathrow. (Peter Macdiarmid/LNP)

A blacked out vehicle at Heathrow Airport reportedly has Prince Harry inside

Prince Harry reportedly touched down at Heathrow Airport on Tuesday, and was driven to Clarence House. (W8Media/MEGA)

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The visit between father and son was brief, as the King was photographed leaving Clarence House shortly after, accompanied by Queen Camilla. According to Sky News, the royals reportedly returned to Buckingham Palace, then are believed to have departed via helicopter for Sandringham.

Earlier in the day, UK Prime Minister Rishi Sunak told the BBC that the monarch's cancer had been "caught early."

King Charles waves out his car window seated next to Queen Camilla as he leaves Clarence House

King Charles waved as he left Clarence House after meeting with his son Prince Harry. (HENRY NICHOLLS/AFP via Getty Images)

Buckingham Palace announced on Monday that during the king's recent hospital stay for an enlarged prostate, "a separate issue of concern was noted" and later identified as cancer.

"His Majesty has today commenced a schedule of regular treatments, during which time he has been advised by doctors to postpone public-facing duties. Throughout this period, His Majesty will continue to undertake State business and official paperwork as usual," a press release said. 

King Charles in a navy suit waves to spectators as he leaves The London Clinic

King Charles left The London Clinic on Jan. 29 after undergoing a corrective procedure for a benign prostate enlargement. (Max Mumby/Indigo/Getty Images)

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

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Prince Harry in a black suit kisses King Charles in a navy suit

King Charles, left, and Prince Harry have had a strained relationship in recent years. (Matt Dunham - WPA Pool/Getty Images)

On Monday, a source told Fox News Digital that the Duke of Sussex had previous communication with his father before the news of his illness went public, explaining, "The duke did speak with his father about his diagnosis."

King Charles waves as he walks alongside Queen Camilla and The Reverend Canon Dr Paul Williams

King Charles III waved to spectators as he walked alongside Queen Camilla and The Reverend Canon Dr Paul Williams, just one day before announcing his cancer diagnosis. (Max Mumby/Indigo/Getty Images)

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On Sunday, King Charles was spotted at a church service, where he waved to spectators while walking alongside his wife Queen Camilla and The Reverend Canon Dr Paul Williams. It was the monarch's first outing since his release from the London Clinic.

The King's hospital stay coincided with daughter-in-law Kate Middleton's own hospitalization for abdominal surgery.