The actor reveals that it was an offhand comment from Julia Louis-Dreyfus about sharing scenes with Heidi Swedberg that led to the character's demise.

If you had trouble understanding why George (Jason Alexander) and Susan (Heidi Swedberg) stayed together on Seinfeld, you weren't the only one. Not that there's anything wrong with that.

Alexander was a guest on Wednesday's Howard Stern Show and admitted that the show's writers decided to kill off Susan with poisonous envelopes because he and the rest of the cast did not enjoy sharing scenes with the actress who portrayed her.

"I couldn't figure out how to play off of her," Alexander said of Swedberg, who followed her 1997 departure from the celebrated NBC sitcom with roles on Roswell, Gilmore Girls and Bones. "Her instincts for doing a scene, where the comedy was, and mine were always misfiring. And she would do something, and I would go, 'OK, I see what she's going to do — I'm going to adjust to her.' And I'd adjust, and then it would change."

Alexander said he wasn't happy when, three episodes into Swedberg's stint on the series, co-creator Larry David informed him that George and Susan would be getting hitched.

"What [David] said was, what Heidi brought to the character is, we could do the most horrible things to her, and the audience was still on my side," Alexander said, laughing.

Later on in the show's run, with producers still unsure of whether Susan and George would go through with the wedding or what her future would be, Jerry Seinfeld (Jerry) and Julia Louis-Dreyfus (Elaine) shared a number of scenes with Swedberg and finally understood what Alexander had been grousing about.

"They go, 'You know what? It's f—ing impossible. It's impossible,'" said Alexander, who stressed that he had nothing against Swedberg personally. "And Julia actually said, 'Don't you want to just kill her?' And Larry went, 'Ka-bang!'" Just like that, the character's fate was sealed (so to speak).

On Thursday, Alexander posted a message to Twitter saying he regretted how his comments to Stern came out, as his intention for telling the story was solely to make it clear that he and the cast did not have issues with Swedberg's personality.

"OK, folks, I feel officially awful," Alexander wrote. "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."

Alexander wrote that Louis-Dreyfus' "kill" comment was about the character, not the actress, and he pointed out that Swedberg would routinely ask him if he had any suggestions for her performance. He also wrote that David and Seinfeld were pleased with how Swedberg was bringing Susan to life: "People clearly liked the [George-Susan] interplay, even though I believed I was 'off.'"

"[Swedberg] was generous and gracious, and I am so mad at myself for retelling this story in any way that would diminish her," Alexander continued. "If I had had more maturity or more security in my own work, I surely would have taken her query and possibly tried to adjust the scenes with her. She surely offered. But, I didn't have that maturity or security."

Alexander's exchange with Stern about Swedberg can be heard below. His follow-up tweet can also be read below.

Oh dear God, leave Heidi alone Read: http://t.co/14Q5akRj38 — jason alexander (@IJasonAlexander) June 4, 2015

June 4 at 8:50 a.m. Updated with Alexander's tweet.

Email: Ryan.Gajewski@THR.com

Twitter: @_RyanGajewski