Ken and Sam knew each other at school. Ken was in the year above Sam and although they weren't necessarily friends, Ken had a bit of a crush on Sam.
They went off to different Universities and then Ken went off travelling before deciding to become a teacher. He knew that Sam was a teacher and got back in touch with her. They met up and the rest, as they say, is history.
Ken popped the question to Sam during a walk at Watership Down on Christmas Eve 2009!