The Official Online RBS 6 Nations Store is open. The store has everything you need to get behind your team during the RBS 6 Nations, plus the store is now fully stocked with a much wider range of rugby merchandise.
The two opposing captains have made three British and Irish Lions tours together - to Australia in 2001, New Zealand in 2005 and South Africa last year.
But friendship and sentiment will be forgotten for Williams as he plans to gatecrash O’Driscoll’s celebrations.
"I think the word legend is thrown around a lot, but he is the epitome of the word,” said Williams.
"He's probably been the best player in the northern hemisphere for the last decade, if not the world and you can't speak highly enough of him.
"I know him off the field as well and he's a really down-to-earth guy."
Williams will celebrate a person milestone of his own on Saturday by winning his 95th cap, taking him one clear of Colin Charvis as Wales' most capped forward.