Charles presented honours from the Royal Victorian Order (RVO) to around 150 sailors and officers who took part in the historic event or planned the Navy's involvement.
Almost 100 Royal Naval Ratings, known as a Sovereign's Guard, pulled the gun carriage carrying the Queen’s coffin as it was borne from Westminster Abbey to Wellington Arch in the capital, and 40 marched behind, acting as a break.
The royal family's Instagram account shared highlights from the open-air ceremony, which you can watch below, showing the King speaking with sailors as they lined up in the Castle quadrangle, accompanied by the Band of the Royal Marines.
"In a special parade and ceremony at Windsor Castle, The King today presented @RoyalNavy personnel with Royal Victorian Order honours, in recognition of the role they played in Queen Elizabeth II’s Funeral Processions," the royal family's Instagram shared in the caption.
Royal fans appeared to be incredibly moved by the King's engagement, with one social media user commenting: "What an honour for these fabulous servicemen and women. How fabulous to see. And their smiles too!"
Another wrote: "Such a precious moment. So well deserved by each and every one of them, they did our wonderful late Queen proud."
A third said: "This is incredibly thoughtful and heartwarming," while a fourth added: "Well deserved. What an amazing job they did. QE2 would have been very proud."
Among those sailors recognised by the monarch was Medical Assistant Paisley Chambers-Smith, who was awarded an RVO silver medal for pulling the gun carriage carrying the Queen's coffin with almost 100 other sailors.
Miss Chambers-Smith is seven months pregnant and wore a blue summer dress for the event as there is no Royal Navy ceremonial maternity wear.
The medic, who works alongside civilian medical staff at the NHS Queen Alexandra Hospital in Portsmouth when not on deployment, said after the open-air ceremony at Windsor Castle: "It's not something I imagined doing so soon in my career.
"The training was so hard but worth it, and on the day it was a massive honour to be there."
The King, who was wearing military uniform, was also mindful that it was unusual to see a heavily pregnant woman on parade.
"He asked when the baby was due and how it is standing in the heat," Miss Chambers-Smith said, adding that the baby is due at the end of July and she intends to start maternity leave in June.
Queen Elizabeth II died at the age of 96 at Balmoral Castle on 8 September 2022. Her state funeral was held at Westminster Abbey in London on 19 September 2022, followed by a committal service at St George's Chapel in Windsor.
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