(CNN)Actor Jason Alexander apologized Thursday for telling Howard Stern that the reason "Seinfeld" co-creator Larry David killed off his character's fiancee in 1996 is that he couldn't figure out how to work with her. "She was generous and gracious, and I am so mad at myself for retelling this story in any way that would diminish her," Alexander said in a Twitter apology to the actress, Heidi Swedberg. Alexander initially told the story Wednesday in an interview with Stern. He said the decision to kill off George Costanza's fiancee, Susan Ross, wasn't just a comedic one. Heidi Swedberg and Jason Alexander in a scene from "Seinfeld." David made the decision after cast members said they couldn't figure out how to work with Swedberg, Alexander said Wednesday. "I love her. She's a terrific girl. I love her," Alexander said of Swedberg. "I couldn't figure out how to play off her. "Her instincts for doing a scene, where the comedy was, and mine were always misfiring," he told Stern. "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 then I'd adjust, and it would change." Alexander told Stern that David and the other actors said he was crazy for thinking scenes with Swedberg weren't working. That's when only he was working with her, Alexander said. When castmate Julia Louis Dreyfus and others began to interact more with the character, they realized the timing was off, too, Alexander said. "And Julia actually said, 'I know it's, just, don't you just want to kill her?' " Alexander said. "And Larry went, 'Kabang! Now we've got to kill her.' " On Thursday, however, Alexander said that Swedberg was always willing to do whatever she could to improve her scenes and blamed himself for any shortcomings. "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," he said. Swedberg didn't immediately respond to a request for comment. Alexander said Thursday in his Twitter post that said the decision to kill off Ross -- by licking cheap wedding invitation envelopes tainted by toxic glue -- was the inventive out that David and star Jerry Seinfeld were looking for to avoid Costanza getting married and not any reflection on Swedberg. "It works perfectly," he said of the on-screen relationship. Alexander said he regretted "putting a heavy burden" on Swedberg, who despite appearing in nearly two dozen television and film projects appears to have moved on to focus on playing and teaching music. "Now everybody, calm down and just enjoy the reruns and think, 'why did he think this wasn't working? This is great,' " Alexander said.