'The Waltons' Actress Mariclare Costello Dead at 90

Mariclare Costello, best known for playing schoolteacher Rosemary Hunter on "The Waltons," has died at 90.

Her family says she passed away April 17 in Brooklyn, closing out a long and impressive career that also includes the 1971 cult horror flick "Let's Scare Jessica to Death," and starring opposite Martin Sheen in the ABC telefilm "The Execution of Private Slovik."

Mariclare was also a familiar face on Broadway in the '60s and '70s ... but TV fans knew her best as Rosemary on 15 episodes of "The Waltons," before she moved on to costar as the family matriarch in the CBS drama "The Fitzpatricks."

She was married to "M*A*S*H" actor Allan Arbus until his death in 2013.

Mariclare Costello was 90.