Betty White may've been known as "America's Sweetheart," but the Hollywood legend allegedly had a mean streak ... this according to fellow actress Sally Struthers.

The "All in the Family" star came out swinging against the "Golden Girls" alum during an appearance on the "Let's Talk About That" podcast ... blasting the late comedy legend as a "very passive-aggressive woman."

Per Sally, she had a less-than-enjoyable encounter working with Betty on a game show pilot.

The actresses connected at BW's house to collaborate on the project ... but things took an ugly turn when Betty "totally fat-shamed" Sally in front of a room full of people.

She recalled ... "I reached for a cookie and she said in front of everyone, ‘Oh, I wouldn't do that if I were you dear, you don't need a cookie.' ... And I thought, ‘Gosh, that's not nice.'"

The experience didn't put her off from the rest of the "Golden Girls" cast, however ... Sally praised Betty's costar Bea Arthur as "a force of nature," after getting the chance to work with her on "All in the Family."

Sally said she never spoke out about Betty previously as she was well aware just how much everyone loved her foe ... but, felt comfortable saying something now the TV personality is dead.