Princess Anne makes King Charles laugh out loud after revealing cheeky nickname for him

The BBC's new documentary titled Charles III: The Coronation Year is teeming with never-before-seen footage of the royal family behind palace doors.

The 90-minute special, which aired on Boxing Day, charts the "landmark moments" in Charles's first year as monarch including the run-up to his coronation, the ceremony itself and events that took place in the months after.

During one particularly heartwarming segment, King Charles'ssweet bond with his sister Princess Anneis captured for all to see.

The encounter took place as key members of the royal family started filtering through Buckingham Palace ahead of their majestic balcony debut.

Amongst the cluster of royals featured in the clip is Princess Anne who can be seen making a beeline for her brother Charles, before calling out, "Hello, old bean".

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Her cheeky greeting prompted King Charles to laugh out loud, suggesting that the unusual moniker used by his sister Anne, is a regular favourite. Amused by the encounter, he proceeded to lovingly shake his sister's hand in a touching display of affection.

The documentary also features commentary from Queen Camilla's lookalike sister, Annabel Elliot. Sharing a glimpse inside the moments immediately after the coronation, Annabel gushed: "There was such an air of celebration".

She went on to say: "It's a cliché, but you could sort of feel the love."

Anne's jovial exchange with Charles quickly caught the attention of avid royal fans on Twitter.

Beneath the clip which was shared to social media, one Twitter user penned: "Princess Anne is just cool. She has a way of her own, and it's very committed and apparent in all she does. Elegance to boot, and a dry wit that keeps it real" while another chimed in: "Such a cute moment!! Love their relationship."

A third remarked: "I keep watching this over and over. It's so lovely to see" and a fourth sweetly added: "They’re so affectionate and have such fun together. It's truly heartwarming and so wonderful to catch a glimpse behind the scenes."

It's been an incredibly busy period for King Charles and his family. On Christmas Day, the royals were out in full force for the annual church service in Sandringham.

Charles, 75, and his wife, Camilla, 76, were in high spirits as they greeted the crowds who had gathered to catch a glimpse of the royals.

Joining them at St Mary Magdalene Church were the Prince and Princess of Wales and their three children, the Duke and Duchess of Edinburgh, Princess Beatrice and her husband Edoardo Mapelli Mozzi, Sarah Ferguson, Princess Anne and Sir Timothy Laurence.

Also in attendance were Princess Eugenie and her husband Jack Brooksbank, Prince Andrew and Zara and Mike Tindall with their daughters Mia and Lena.