I didn't watch it, mainly because I can't stand him either, although I have read reviews of the programme. I expect the BBC thought it would make good viewing.
My husband is currently doing his family tree and has traced his family back - sometimes through the female line - to Robert the Bruce and further. Everyone is related because mathematically, if you double your grandparents, great-grandparents etc back through time, you eventually reach a stage where you have more ancestors than the population of the country at that time. So, if you're of British origin, you'll probably be related to Edward III too. The same rule will apply in other countries.