A recent post on the excellent Reading Raving and Ranting Blog about Gilbert le Despenser led to some interesting questions about the Despenser line and whether or not Princess Diana was related. Well, to cut to the chase the male line of the Despensers died out circa 1413, although there are many descendants to this day through the female line.
As to the link with the Spencers of Althorp, 'tis a myth. One of several created by dodgy Tudor heralds in return for a lined pocket.
I think I once came across a source that stated Princess Diana was descended from Constance of York, but I'm not sure of the route. Possibly through the Audleys, as Constance's descendants through that lot are legion. They include people as diverse as Robert E. Lee and Humphrey Bogart. But it's just possible Diana was descended from the Despensers after all. If anyone's interested, please do the research.
As an aside, I've been delving into my ancestry on and off for a few years now, but find they're a pretty boring lot - not a pirate or murderer among the lot of 'em. Very disappointing. You'd have thought at least one of them could have had the decency to get himself hanged. The most promising claim to fame is that I may be related to one of Charles II's minor mistresses, Katherine Pegg. Though I've not quite made the link, we seem to come from the same root, the Peggs of Ashbourne.