I've found the sword... i've went to the cave to unlock its stuff... the sword is activated in a thing... i cleared the whole cave... and yet nothing popped up saying i completed anything?

After killing the Boss guy... i picked up a flaming sword? is that the sword says something like honed something something that does fire damage

P.S i left the original sword still in the activation part at the start?

???

The quest is marked completed, when you insert the sword in to the alter. So check your journal to see if the quest is marked completed, cause it should be.

if you take the sword back it's higher level and has changed name.

putting the sword in the stone completed the quest... the rest is just a little bit of looting and killing.

this...i would just leave the sword in the stone and never return to the redoubt or read lost legends again as the quest will reactivate and the briar heart will have the sword again(bug)

fyi i got rid of the extra red eagle quest sword by mounting it in my solitude basemant