“He wrote to Camilla and pleaded with her to reconsider, but I think by this point, it was just too late.”

King Charles had to take “urgent action” after uncovering shattering news about Camilla while on naval duty overseas in a devastating letter, a documentary has revealed.

The Channel 5 show, ‘Charles and Camilla: 20 Years Married – A Royal Love Story’, shows viewers the early days of their romance, predating her time as Mrs Parker Bowles.

According to the new doc, a young Charles was serving with the Royal Navy in the 1970s, far away from Camilla, when he received a bombshell letter which flipped his world “upside down”.

The announcement of Camilla’s engagement to Andrew Parker Bowles shook Charles, leading him to respond swiftly with an onslaught of “urgent action” letters, insiders claim.

Royal writer Penny Junor, familiar for titles like ‘All The Queen’s Corgis’ and ‘The Duchess: Camilla Parker Bowles and the Love Affair That Rocked the Crown’ said: “He was absolutely devastated, heartbroken.”

Katie Nicholl, royal correspondent for Vanity Fair, added: “He wrote to Camilla and pleaded with her to reconsider, but I think by this point, it was just too late.”

Penny Junor sums up the King’s emotions, remarking: “She was, I think, his first real love, and when you fall first, sometimes you fall hardest.”

King Charles and Queen Camilla’s love story, which has spanned decades, began in the ’70s at a polo game. Camilla was on a break from her then-beau Andrew Parker Bowles who had also dated Charles’ sister, Princess Anne, reports the Mirror.

However, Camilla and Charles’ romance was interrupted as duty called, and Charles had to ship off for Navy training. Camilla went on to reunite and marry Andrew in 1973. Meanwhile, Charles famously wed Lady Diana Spencer.

Yet, Camilla’s relationship wouldn’t last, as the couple divorced in 1995. Meanwhile, Charles and Diana finalised their divorce in 1996, and just a year later, in 1997, Diana tragically died.

Against all odds, King Charles and Queen Camilla finally said ‘I do’ in a civil ceremony at Windsor in 2005, with the late Queen Elizabeth II throwing them a grand reception held at Windsor Castle.

Commenting on Charles and Camilla’s unlikely nuptials, royal expert Hugo Vickers divulged to OK! Magazine: “For a long time, people like me would have told you there was absolutely no way Charles could marry Camilla, that it was absolutely out of the question and wasn’t going to happen,” only to admit: “But it did happen and it worked.”

“From the moment he met her, he seemed struck by her,” says Hugo. “Obviously, they just clicked and it’s clear that something about her appealed to him very early on.”

Charles & Camilla: 20 Years Married – A Royal Love Story airs tonight at 9.15pm on 5.