You can get this achievement by joining the Dragon Remnants covenant.
Note: possible storyline spoilers below...
*** Spoiler - click to reveal ***To join the covenant, you must first obtain the Petrified Egg from the Dragon Shrine, which is a required location towards the end of the game.
About halfway through the level, you'll come across 2 chests located in a lower area you must jump down to (note: one chest is a mimic). The exit out of this area takes you through another room containing a large hammer knight. After this, you'll ascend some stairs and be invaded by an NPC red phantom. The Petrified Egg is in this room in plain sight.
Take the egg to Magerold of Lanafir in Iron Keep (the merchant on the first right after entering). Give the egg to him, and a new dialogue option will now be available to enter the covenant.
Note: Like all other covenant achievements, you don't actually have to join for the achievement to unlock.