Princess Diana met Charles for the first time when he was dating her sister Sarah, but after that, she was sure that she wanted to be his wife.
Princess Diana and Prince Charles had one of the most (in)famous marriages and, eventually, divorces in the world. They married on July 29, 1981, and it was watched by a global television audience of 750 million in 74 countries. In Britain, where a public holiday had been declared, as many as 28.4 million watched on BBC and ITV while 600,000 people were on the streets of London to celebrate.
When it came crashing down less than two decades later, that too was public. The princess and prince had many differences and the first among them was their huge age gap. Prince Charles was 32 when he began courting a then 19-year-old Diana Spencer. Prior to that, he had met her in 1977 when he dated her sister, Sarah. This relationship was shortlived because the duo was not compatible. Sarah, who went on to marry Neil McCorquodale, reportedly said she wouldn’t marry Charles "if he were the dustman or the King of England," as per Town & Country.
Young and impressionable, Diana was only 16 then and apparently besotted by Charles. She had met him only twice and yet she decided that the heir to the throne would be her life partner. The reason for that was quite heartbreaking because it shows how much her broken family had pained her. She had confessed to her friends about her desire to marry Charles, wrote Tina Brown in her book The Diana Chronicles, as per Reader's Digest.
Another royal commentator, Howard Hodgson wrote in the 2007 biography, Charles: The man who will be King, that Diana first revealed her intentions when she went skiing in the French Alps. "One of those present at the time was to recall years later to Clayton and Craig that she was determined to realise her destiny," as per Express UK. Tim Clayton and Phil Craig released a biography of Diana back in 2001, called Diana: Story of a Princess. Their source had said, "She was going to get married to the Prince of Wales — not 'I want to' or 'I'd like to' but 'I’m going to'... She was extremely sure of herself."
When the source asked her, "Why would you want to do that? What’s the attraction?" the princess reportedly said, "He’s the one man on the planet who’s not allowed to divorce me."
Divorce used to be a taboo matter in the royal family and it was expected that the future king wouldn't separate from his wife. Prince Charles was able to marry Camilla Parker Bowles, another divorcee, later because of a change in the law that took place with the UK now subscribing to the European Convention of Human Rights (ECHR). Under the ECHR,
the Human Rights Act 1998 enshrines the right to marry under Article 12 of the Convention. Governments can't place arbitrary restrictions on people of marriageable age.
The next time Charles and Diana met was when she was 18.5 years old. "I was asked to stay with some friends in Sussex and they said, 'Oh, the Prince of Wales is staying,' and I thought I hadn’t seen him in ages," she told her speech coach, who secretly recorded it on a tape that was later used for the Channel 4 documentary Diana: In Her Own Words. "He’d just broken up with his girlfriend and his friend Mountbatten had just been killed. I said it would be nice to see him. I was so unimpressed. I sat there and this man walked in and I thought, well, I am quite impressed this time round. I was different."
Their romance was a whirlwind since they only met 12 times before getting engaged and the rest is history. But, why did it matter to Diana that he couldn't divorce her? A daughter of a family that was broken up by divorce, she wanted none of that in her life. She was only seven when her mother, Frances Spencer, left her father, John, and her five children in his care. She was the fourth of five siblings.
Frances went on to marry Peter Shand Kydd in 1969 and John won custody of the children. He later remarried and settled down with Raine, Countess of Dartmouth, but Raine wasn't the stepmother Diana or her siblings could be comfortable with.
As per Express, her speech coach had also recorded her as saying, "I was always told by my family that I was the thick one, that I was stupid and my brother was the clever one." She also said that they never told her that they loved her.
With a painful childhood, it makes sense that she wanted a man who wouldn't leave her to be alone. Unfortunately, her marriage didn't last and they separated in 1992 and eventually divorcing in 1996, the very thing that a young Diana never wanted.
References:
https://www.rd.com/advice/relationships/what-diana-first-thought-of-charles/