Jason Alexander finally revealed on Wednesday, June 3, why his on-screen fiancee Susan was killed off the sitcom in 1997, and issued an apology to actress Heidi Swedberg for sharing that secret. Credit: Tiffany Rose/Getty Images

Good riddance from George Costanza! Jason Alexander apologized on Thursday, June 4 to his Seinfeld costar Heidi Swedberg after finally revealing the reason why his on-screen fiancee was killed off the sitcom in 1997.

"I couldn't figure out how to play off of her," Alexander, 55, told Howard Stern on the shock jock's SiriusXM radio show on Wednesday. "Her instincts for doing a scene, where the comedy was, and mine were always misfiring. And she would do something, and I would go, 'Okay, I see what she's going to do — I'm going to adjust to her.' And I'd adjust, and then it would change."

The actor recalled how he was not pleased when the series' co-creator Larry David told him that George Costanza was marrying Susan. "We could do the most horrible things to her, and the audience was still on my side," Alexander said with a laugh.

While Alexander openly griped about sharing scenes with Swedberg, his other costars including Jerry Seinfeld and Julia Louis-Dreyfus (who had their own mini reunion on Wednesday night!) slowly caught on, too.

"They go, 'You know what? It's f—ing impossible. It's impossible,'" Alexander recalled of his fellow comics working on scenes with Swedberg. "And Julia actually said, 'Don't you want to just kill her?' And Larry went, 'Ka-bang!'"

Susan ultimately met the grim reaper while licking wedding invite envelopes — which were tainted with toxic glue. Despite the backstory, Alexander insisted that he liked Swedberg, who went on to act in Gilmore Girls, Roswell, and Bones. Occasionally, their circles would overlap and Alexander confessed that it was "a little awkward" seeing her.

What's even more awkward, though, was the backlash he faced after making the remarks on the Stern show.

On Thursday, Alexander apologized to Swedberg in an elaborate Twitter post for publicly revealing that insider scoop. "Ok folks, I feel officially awful. Yesterday on @Sternshow, I retold a story I had told years ago about my personal difficulties and insecurities in playing George against the Susan that Heidi Swedberg created," he shared. "The impetus for telling this story was that Howard said, 'Julia Louis-Dreyfus told me you all wanted to kill her.' So I told the story to try and clarify that no one wanted to kill Heidi."

He went on to say that the cast "really liked and like Heidi," describing her as a "kind, lovely person who undoubtedly worked really hard to create Susan."

"To Heidi, I personally apologize. You are a sweetheart," Alexander noted. "I actually launched into this on Stern to defend you. But this is why I'm not a lawyer. Now everybody, calm down and just enjoy the reruns and think, 'why did he think this wasn't working? This is great.'"

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