By Peter Hunt
BBC Royal correspondent
It was a relationship which developed and flourished at university, but which has now foundered outside in the "real" world.
The pair were often seen as a couple in public
Life at St Andrews for Kate Middleton and especially, Prince William, was a cocoon. They were pretty much left alone by the media.
As William said once, he could go undisturbed to the supermarket to buy his asparagus.
He felt protected and relaxed in the remote Scottish town sharing his student digs with the girlfriend who is credited with persuading him not to leave when he had a "wobble" at the end of his first year.
Following his career
Graduation in 2005 brought, as they must have known, fresh challenges. Prince William was in no rush to get married. In his one public comment on the subject he talked about 28 or 30 being a good age for him to tie the knot.
He is a young man who's determined to remain in control of his life - a life dominated by the destiny he will one day fulfil.
In the short term, he is following his army career.
Kate Middleton, on the other hand, was in a sort of royal limbo - without the security or indeed the restrictions that an engagement would have provided and imposed.
The young woman from Berkshire - whose parents were the millionaire owners of a mail order business - might have been a "royal bride-in-waiting", but she was still a private citizen. Initially, she struggled to find a job which would not attract adverse comment.
They tried to lead a "normal" life - doing things "normal" couples would do - a challenge, though, when one half of the partnership is second-in-line to the throne.
When Kate attended William's graduation from Sandhurst it was interpreted as a significant step - a sign of the seriousness of the relationship.
Kate appeared relaxed when photographed at such public occasions - less so, when snapped putting her rubbish out or going to work.
Before the split, her lawyers had worked hard to convince the media to leave her alone when she was without William going about her everyday business.
Now, they have decided the status quo - with no engagement or a hint of one in the near future - is unsustainable.
The young couple - Kate's 25, William's 24 - are going their separate ways.
He must know, from his father's experience in the Seventies, that from now on every woman he is seen with will be assessed in some quarters as a potential future queen.
Kate Middleton, rather like Koo Stark before her, has secured an undesired place in the history books as the ex-girlfriend of a prince.