My new sword was great, but Vendrick's sword was still bigger. He kept killing me and I kept coming back for more to the point where the baddies in between the bonfire and his boss chamber stopped spawning, just like at the dragon shrine. I don't know why it took me so long to work out but - my mistake in this fight turned out to be EVADING. Or at least, evading at the wrong time (vertical attacks = wrong time).
It's always the simplest solutions...
Instead of rolling, or blocking (because, good luck with that) I just needed to run and be point blank to the old king at all times. With that strategy, I probably would have won with a dagger *face palm*. Strangely Vendrick didn't drop a crown, not that it mattered much to me. I headed back to the castle to report to Queen Nashandra only to find she wasn't on her throne.
Curious, I looked around and was joined by Pilgrim Bellclaire, who I suppose was adventuring. It's cool that wearing the king's ring makes all the previously hostile statue knights dormant so we could explore at our leisure. In the basement was a big locked door I totally forgot about. Behind it was the Throne of Want, and the Emerald Herald (erm, how the heck did you get in here). After telling me her real name is Shanalotte, she advises me that Nashandra is going to come after me once I approach the throne. Thanks for the heads up!