It was Lasko who demanded Letterman's second public apology on Monday, FOXNews.com has learned.
Letterman addressed his wife directly during the taping of Monday's “Late Show.” He said she had been “horribly hurt by my behavior” and stated flatly that his affairs “are in the past.”
He vowed to repair his relationship with Lasko, whom he married in March after a years-long courtship.
"Let me tell you folks, I got my work cut out for me," he said ruefully.
But a source close to Lasko, 48, told FOXNews.com that the Monday apology "wasn’t something Dave wanted to do at all.”
“He wanted the whole thing to blow over," said the source. "But Regina told him he better make an apology to let everyone know how sorry he was for how much he hurt and humiliated her.”
According to the source, she demanded that he go over with her exactly what he was going to tell viewers and studio audience members on Monday. She was even willing to allow him to make “one or two jokes to be a part of it as long as they weren’t at her expense.”
But Lasko was not laughing when Letterman took her concession too far, throwing in more than the agreed-upon one or two wisecracks about his affairs.
“Regina felt like Dave’s humorous take on the apology lessened the sincerity of it, and she’s not happy at all,” says the source.
A rep for Letterman declined to comment Thursday.
Lasko has remained largely in the background during the scandal, and her husband rarely mentions her on the show.
When Letterman announced his March 2009 wedding to his studio audience, he said he and the former “Late Show” staffer had been dating since 1986. She reportedly moved in with him in 2001; the couple have a 5-year-old son.
When Letterman made his marriage announcement, he stayed true to character, poking fun at his decision to wed during his monologue.
“I had avoided getting married pretty good for, like, 23 years,” he said, “and I … secretly felt that men who were married admired me, like I was the last of the real gunslingers.”
On the day of the wedding, which took place in Montana, Letterman said the couple’s car got stuck in the mud, which he took to be a sign that he was making the wrong decision.
But while Lasko could stand jokes about their nuptials, it looks like she has drawn the line at cracks about his affairs.
The Associated Press contributed to this report.