Howard Stern asked Jason Alexander a burning question that was never quite answered after season 7 of Seinfeld -- why did George's fiancee die so suddenly?

On the {i:Howard Stern Show} Wednesday, 55-year-old Alexander said the duo's chemistry didn't match. "The actress is this wonderful girl Heidi Swedberg," he told Stern anxiously before dropping the truth. "I couldn't figure out how to play off of her," he admitted.

Swedberg, who played George's love interest Susan Ross, was killed-off the show suddenly -- and before an on-screen wedding -- after licking toxic glue on her wedding invitation envelopes.

"Her instincts for doing a scene, where the comedy was, and mine, were always misfiring," Alexander said. "She would do something, and I would go, 'OK, I see what she's going to do,' I'll adjust to her. And then it would change."

None of the other Seinfeld cast or crew members quite understood Alexander's problem, but he says that's because he had the most air time with Swedberg. Only until co-stars Jerry Seinfeld and Julia Louis-Dreyfus worked on scenes with her for a week did they understand.

"You know what? It's [expletive] impossible!" Alexander reveals Seinfeld said afterward. He credits Dreyfus with the idea of killing her off.

Although the pair's on-screen chemistry was always a little off, Alexander still has warm feelings toward Swedberg. "Every time I tell this story I cringe, because Heidi is the sweetest person ever," Alexander said.