Prince William and Kate Middleton formalized their relationship after getting married in 2011. However, the royal couple somehow knew that they would eventually walk down the aisle together back in 2007.
Royal expert and biographer Katie Nicholl revealed in her book "Kate: The Future Queen" that Kate and Will made a secret pact with regards to their future together when reunited after briefly breaking up in 2007.
According to Nicholl, the couple went on a romantic vacation to the luxurious island of Desroches in the Seychelles where they made a promise about their long-term future together.
"There on the paradise island, William promised Kate that he was in the relationship for the long term. For the very first time, they talked seriously about marriage, and with the ocean before them and beneath the night sky, they made a pact to marry."
Kate wanted some assurance about their future, but Prince William wasn't ready to get wedded just yet. According to someone close to the two, the couple agreed and decided to wait until Will felt ready.
"They didn't agree to get married there and then; what they made was a pact. William told Kate she was the one but he was not ready to get married. He promised her his commitment and said he would not let her down, and she, in turn, agreed to wait for him." the source told Nicholl.
The royal couple may have gone through ups and downs during the process, but the promise they made to each other remained unyielding. At the time, Prince William's commitment that he would not let Kate down came into reality. After a few years of keeping each other’s promise, Kate and Will officially sealed their pact in the form of a grand royal wedding back in 2011.