I've yet to start Hardmode myself. Waiting on my friends to ding first. xD

But, from the posts on the forums, I think it goes like: 50-AF-Story-Wanderer's Palace-Ifrit HM-Some Darklight-AK-More Darklight-Other Primals Hardmode-Coil

Somewhere in that the Relic weapon should be, not sure where. :P

Ah, user above me did much better.