Prince William and Kate Middleton's love story may be the sweetest one but, just like other couples, it never goes without trials and challenges. Before the two made a vow, the Duke of Cambridge asked his wife's father, Michael Middleton, to keep a secret to avoid Queen Elizabeth II's anger.

Kate and Prince William first met at the University of St. Andrews in Fife, Scotland. After being friends for a year, they moved together in a house with two other students. From here, a romance bloomed. On the day of their graduation, Michael took a photo of them where they looked very much in love with each other. 

Despite having an on-again-off-again relationship, Prince William decided to ask for Kate's hand in 2010. Royal author Kate Nicholl wrote in Vanity Fair that William asked for Prince Charles' help, and his father gladly gave his support.

Prince Charles even let the Middletons stayed in Birkhall and used his private car. Prince William, on the other hand, arranged a private shooting lesson for them. It was the first time for Kate's parents to go to the Queen's private estate.

One night, just before dinner, Prince William took Michael's side. "In the tartan-furnished drawing-room, which is exactly the late Queen Mother left it," the second in line on the throne asked the Middleton patriarch for permission to marry Kate.

Michael granted Prince William's request immediately. However, the latter made Kate's dad swore to keep the engagement a secret first. At the time, the couple didn't want anyone to know about the betrothal as William hadn't said anything about it to Prince Charles and Queen Elizabeth yet.

This way, they could avoid Queen Elizabeth's fury. According to Express, even though Her Majesty knew Prince William took Princess Diana's ring, she was still waiting for her grandson to inform her about it. As the head of state, she still needed to be formally informed of any official marriage announcement.

If they didn't, it would be a breach in protocol. Prince William counted on Michael, and the latter didn't fail him. He kept the news of engagement a big secret.

However, when the Middletons' photos at the Balmoral emerged, it caused a frenzy of excitement, doubting the two were already engaged. Later, an official announcement about Prince William and Kate's engagement was formally made.

To cap off their intense engagement, Prince William and Kate finally tied the knot at Westminster Abbey in 2011. Thousands of people witness their wedding ceremony. It was even televised all over the world.