Princess Diana said Charles 'broke her heart' with cruel phone call ahead of wedding

Prince Charles and Princess Diana's marriage was a very complicated one, and their troubles started before they even said I Do.

The heir to the throne was reportedly under a huge amount of pressure to find a royal wife and settle down, so popped the question in February 1981 after meeting Lady Spencer just 12 times.

Diana, who was just 20 at the time, nervously laughed when her boyfriend got down on one knee in the nursery at Windsor Castle - but she was delighted to place the stunning sapphire engagement ring on her finger.

Shortly afterwards the couple shared their happy news with the world and well-wishers started counting down the days until their Royal Wedding.

And while people couldn't get enough of what appeared to be their fairytale love story, things were very different behind the scenes.

But as the wedding planning began Charles had to go about his royal duties as normal, and left for a tour of Australia and New Zealand just a few weeks later.

Saying goodbye at such an exciting time should have been difficult for the couple, but years later Diana admitted that something he did that day "broke her heart".

Royal expert Anthony Holden wrote in his book Charles: A Biography that when the future princess went to say her goodbyes to Charles, the phone rang.

He claims it was Camilla.

Rather than ignoring the call and finishing their goodbyes, Charles is said to have picked up.

Diana walked out of the room and the Prince simply started a conversation with Diana.

Holden writes: "[Diana] was weeping because her last minutes alone with the prince at the palace had been interrupted by a phone call.

"It was Camilla, wanting her own fond farewell. So tender was the conversation that Diana had felt obliged to leave.

"That moment, she said 10 years later, ‘just broke my heart.'”

Looking back at the early days of the couple's relationship with the power of hindsight, there are signs that everything wasn't as perfect as people hoped.

Former BBC News anchor Angela Rippon sat down with the couple for their final interview before the wedding.

She watched it back for the first time for the Channel 5 documentary Charles and Di: The Truth Behind their Wedding.

She said: "With the knowledge of hindsight you read so much more into body language, what was said, looks that were given, reactions.

"That's the value of hindsight isn't it?"

But the final few moments of the interview really stand out to her, when she wishes the couple a lifetime of happiness.

Charles looks Diana, but she looks down at the floor.

"That expression on Diana's face at the end speaks volumes.

"Maybe we should have read so much more into that five seconds at the end the interview. It might have told us so much more about what was to come."

Before they went in they were given a briefing by the Queen's press secretary Michael Shea.

He told them very firmly that the interview would be ended if they asked any questions that had not been agreed.

During the interview Michael stood directly behind Angela out of camera shot, but in Diana's eyeline.

"I'm not quite sure how comfortable it made her feel.

"I got the impression that Princes Charles was very protective towards her.

"Lady Diana was almost slumped in the chair, she was in new territory. She was out of her depth.

"Put any 20-year-old in front of a television camera and say this is an interview about what could be one of the most important days of your life and it's going to be seen by hundreds of millions of people around the world, and there is this man standing behind the person interviewing you making sure you get it right.

"Crikey, anyone would be nervous."