RIP. Marcia Wallace.The voice of Bart's teacher Edna Krabopple passed away this morning.More Like This
Also, there's been speculation a 'beloved character was passing away' later this season, or early next season, but Al Jean (showrunner) confirmed Edna was NOT the character:
"Earlier we had discussed a potential storyline in which a character passed away," Jean said. "This was not Marcia's Edna Krabappel. Marcia's passing is unrelated and again, a terrible loss for all who had the pleasure of knowing her."