Jessica Simpson is reacting to her ex-husband Nick Lachey's headline-making joke about her father during his 2013 appearance on Watch What Happens Live With Andy Cohen.

Simpson recently sat down for a SiriusXM Town Hall with Andy Cohen to discuss her new memoir, Open Book, which airs on Radio Andy on Friday. Cohen brought up Lachey's past appearance on his show, when during the Plead the Fifth segment, he made a joke about his ex father-in-law, Joe Simpson.

When Cohen asked, "What's the best thing about no longer having Joe Simpson as a father-in-law?," Lachey replied, "Umm… I don't have to play grab-a** under the table on Easter Sunday!"

At the time, there had been tabloid rumors that Joe was gay following his 2012 split from Simpson's mother, Tina, after 34 years of marriage. TMZ reported in November 2012 that Joe called the rumors about his sexuality "ridiculous." He also publicly denied on Twitter in February 2014 that he was dating male model Jonathan Keith, with whom he had been photographed, explaining that Keith was his client.

In Simpson's interview with Cohen, she acknowledged that she was "very" pissed at Lachey's comment.

"That was low and that's, like, not for him to talk about by any means because he's not connected with us at all anymore," she says.

Simpson said she did not reach out to Lachey after his comment.

"He was just bitter, you know?" she says. "He was just trying to take a dig."

In her memoir, Simpson writes that Joe was actually against her marriage to Lachey from the start, and cried while walking her down the aisle at her 2002 wedding to the 98 Degrees frontman. Simpson and Lachey eventually separated in 2005.

The 39-year-old singer gets candid in her book about her bumpy relationship with her father, particularly, her feelings when he decided to bring Keith to her July 2014 wedding to Eric Johnson.

"My father called me three days before we left for the wedding to tell me he was bringing his friend Jonathan, a young model he often shot for his new photography business," she writes. "I reminded myself that I needed to accept my father for who he was as he worked it out in real-time… I wasn’t sure how to handle my father now, so I worked with the information he was ready to give me. Maybe I wasn’t ready to listen, I don’t know."

Meanwhile, ET recently sat down with Simpson, and she did have kind words for 46-year-old Lachey almost 14 years after their divorce. She noted that she was, in fact, "madly in love" with Lachey when they married, but was now "happy" that he moved on with Vanessa Minnillo.

"I mean, we just grew apart in so many ways and, you know, we both were at fault in a lot of things, but I mean, I'm happy for him now," she reflected. "He's married with three beautiful children and, you know, that was his purpose, and he took heartbreak and made it into something beautiful and that's what I did as well. But, you know, it took me longer to get there."

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