Queen Elizabeth had 'reservations' about King Charles and Diana's union, wanted her to marry Prince Andrew instead
The Queen preferred Diana to marry Prince Andrew, Charles's younger brother, thinking they might be better suited.
Just before her wedding to Prince Charles, Diana attended a party at Windsor Castle for Prince Andrew's 21st birthday. According to royal biographer Ingrid Seward, Diana wanted to dance with Charles, but he seemed uninterested. Eventually, she danced with others and even found herself dancing alone. Seward describes Diana as "looking exhausted and lost in her thoughts yet still moving in slow, rhythmic time to some tune in her head."

Midnight escape:
Distraught and angry, Diana left Windsor Castle at 5:30 am and went to her father's home. She expressed her unwillingness to marry Charles. However, her father, Earl Spencer, convinced her to change her mind. Seward reveals, "As far as Diana was concerned, the Royal Wedding was off."
The Queen's doubts:
Queen Elizabeth reportedly had reservations about Diana marrying Charles. Seward explains, "The Queen wondered whether anyone that young could differentiate between the man and the prince." Surprisingly, the Queen preferred Diana to marry Prince Andrew, Charles's younger brother, thinking they might be better suited.
Balmoral impressions:
During a visit to Balmoral, Diana enchanted everyone, except, perhaps, the Queen. While Charles found her "marvellous," the Queen harboured doubts. Seward suggests that the Queen had concerns about Diana adapting to royal life and whether she truly understood the complexities of marrying a future king.
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Post-proposal struggles:
After Charles proposed, Diana faced challenges adapting to royal rituals and expectations. Prince Edward's footman, Mark Simpson, became her confidant. Diana opened up about feeling neglected by Charles. Despite initial tensions, Diana turned to the Queen when her marriage started crumbling, but these meetings left the Queen "drained, despondent, and confused."
While Diana eventually married Charles, the journey was far from smooth. The Queen's preferred match of Diana with Prince Andrew could have led to a different royal love story. History, however, had different plans, and Diana's marriage to Charles eventually came to an end in 1996, concluding a chapter in royal history that captivated the world.