The Crown introduced Kate Middleton as a character in the second part of season 6, and one of the most ardent questions viewers might have is how long after the series' end she and Prince William got married. Season 6, which is the show's last, brought the action of The Crown into the 21st century, but its events didn't get too close to the present day. The series' storyline ended in 2005, and it didn't reveal whether Prince William and Kate Middleton got married.
https://screenrant.com/how-long-after-the-crown-season-6-prince-william-kate-middleton-wedding/