Astoria Malfoy's ancestor

"We were capable of having children, but Astoria was frail. A blood malediction, a serious one. An ancestor was cursed... it showed up in her. You know how these things can resurface after generations..."

- Draco Malfoy

This individual was an ancestor of the Greengrass family who was the object of a blood-bourne curse. Resurfacing after generations, the curse was responsible for Astoria Malfoy's frailty and untimely death.