In 2008, Prince William and Kate Middleton had already been dating for several years. Between 2005 and 2008, William trained at the Royal Military Academy Sandhurst before joining the Household Cavalry. After that, he could have left the military entirely in order to serve as a working royal, which is another reason why many people thought he might choose that time to propose to Kate.
According to one royal author, Kate also thought that William would propose to her at that time - but he instead chose to announce he would be joining the RAF Search and Rescue Force.
