Being royal comes with a lot of rules, but sometimes, the members of the royal family decide to go against the grain and break them. Prince Harry and Meghan Markle are thought of as the more unconventional royal couple, with their PDA and modern wedding decisions, like Meghan walking herself partway down the aisle. Prince William and Kate Middleton were also a little unconventional when it cam to their wedding in 2011, it turns out.
According to Express, Will and Kate stayed overnight in Buckingham Palace after their day of wedding festivities (which included a televised ceremony and several parties, just like Harry and Meghan's). It might not seem like a big deal (except, you know, that it's Will's grandma's house which is admittedly a little weird for anyone celebrating their first night as a married couple), but it is. Royals traditionally leave for their honeymoon on the day of their wedding.
For context, when Queen Elizabeth and Prince Philip were married in November 1947, they spent their first night as a married couple in Broadlands, Hampshire. In 1973, Princess Anne and Mark Phillips left immediately for a honeymoon cruise on the Royal Yacht Britannia after their wedding day balcony appearance. As of now, it's still unknown where Prince Harry and Meghan Markle spent their wedding night when they tied the knot in May.
Will and Kate had a good reason for bucking tradition in this case, however—Will had to work right after the wedding. At the time, Will worked as a search-and-rescue pilot (he's since given up the job to focus on royal duties full time) and the couple wasn't able to leave for a honeymoon until 10 days after the wedding. The trip was worth the wait though; Will and Kate honeymooned on a private island in Seychelles.