What is the "best" weapon against Old King Allant?

As the title says. I'm stuck, usually dead within 1 min. Bonesmasher is slow af, just got the "moonlight" sword. This is the first souls like I play, and apart from the old hero I've never been stuck with a boss. (After I learned that I need to be behind him and can't run it was easy.)

EDIT: I DID IT! oh my god that was hard . The trick was broke his "AOE" or what is that charge up. Used like 30 heal grass and had a ~160 heart rate but I did it. First souls game that I've played and finished.

Omw to buy DS3