The no-nonsense member of the wider Royal Family has often been pictured during public events laughing with the monarch and displaying her affection for him.
Body language expert Judi James previously described the bond between the uncle and niece as one of the "sweetest and most uncomplicated" in the Firm.
A similar fondness and special relationship goes back years, and may even be rooted in the King playing a role in choosing Zara's name.
Princess Anne - Zara's mother and Charles's sister - previously recalled: "The baby made a rather sudden and positive arrival, and my brother thought Zara was an appropriate name."
Zara Tindall and King Charles share a close bond (Image: GETTY)
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Known to love history and literature, King Charles approved of a Greek name meaning "bright as the dawn".
The monarch is also known to share a very good bond with his only sister who, two years younger than him, is believed to be one of his closest confidants.
Zara, who was never given a royal title in accordance with her mother's desire to give her the freedom to choose her path in life, often appears at family functions and horseracing events such as Royal Ascot and Cheltenham Festival.
And it is during similar gatherings that the public can see how close Zara and King Charles are.
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King Charles played a role in naming Zara Tindall (Image: GETTY)
Speaking with Express.co.uk last year, Ms James added: "Unlike many of the people in the King’s life, Zara seems to treat her uncle with unfiltered fondness and he seems to respond in kind.
"Their public displays of affection (PDAs) are legendary and the body language signals suggest they are always led by Zara, who seems untroubled by protocol, status or even Charles’s customary avoidance of any touch rituals in public that go beyond a handshake.
"She seems purely keen to show everyone how determined she is to give this sometimes solitary and reflective man a hug."