However William wanted to do things differently, and decided to ditch the custom followed by his father and all his older relatives and appoint Prince Harry as his best man.
According to The Times, William would not have married without Harry by his side, as the brothers had been through so much together.
Calling his brother best man, "had more relevance to his life than the alternative", The Times wrote.
After being appointed best man, Prince Harry was said to be "delighted" with his brother's choice.
Speaking in 2011, Harry said: "It means I get a sister, which I have always wanted."
When it came to his own marriage to Meghan Markle on May 19, 2018, Harry asked William to return the favour, and stand as his best man rather than supporter.
While Prince Charles also had his younger brothers Prince Andrew and Prince Edward involved in his wedding day, they were called supporters rather than best men.