They honeymooned on board the royal yacht Britannia

After Prince Charles and Princess Diana’s “wedding of the century” at St Paul’s Cathedral in July 1981, the royal pair set off for Gibraltar on Spain’s south coast, where they boarded the Royal Yacht Britannia. The yacht cruised around the Mediterranean, including the Greek islands, for 14 days. The couple ended their getaway at Balmoral Castle in Scotland. It was a luxurious itinerary – but what really went down during those first few days of the couple’s doomed marriage? Turns out, a lot more drama than you might think.
Diana was still reeling over this engagement comment

While most people head out on their honeymoon with the impression that their partner is totally in love with them, Diana wasn’t so sure. Her insecurity stemmed from an awkward interview at the time of her and Charles’ engagement. “We had this ghastly interview the day we announced our engagement,” she told her speech coach on a tape that was later used for the Channel 4 documentary Diana: In Her Own Words. “And this ridiculous [news] man said, ‘Are you in love?’ “I thought, what a thick question. So I said, ‘Yes, of course, we are,’ and Charles turned round and said, ‘Whatever love means.’ And that threw me completely. I thought, what a strange answer. It traumatised me.”
Charles called Camilla every chance he got

Although Charles’ former flame Camilla Parker Bowles had already been married to her first husband, Andrew Parker Bowles, for eight years, Charles still found a way to call her from the Mediterranean. “The Prince simply had to be in constant contact with Camilla or he couldn’t function properly,” his valet Stephen Barry said in the book The Diana Chronicles. “If he went without his daily phone call, he would become tetchy and ill-tempered.”