SPOILER ALERT: This story contains spoilers for “Stadium,” Episode 6 of “ The Testaments ,” now streaming on Hulu.

It’s been clear since the beginning of Hulu’s “The Testaments” that Aunt Vidala (played by Mabel Li ) is not Aunt Lydia’s ( Ann Dowd ) biggest fan — and now we know why.

During this week’s episode of Hulu’s “The Handmaid’s Tale” followup series, more backstory is revealed for Lydia — whom “Handmaid’s” viewers came to learn much about over that show’s six-season run — including the fact she actually created the Aunts program in Gilead to save herself in the early days.…