Jessica Simpson is definitely not a daddy's girl.

When Tina Simpson filed for divorce from her husband, Joe Simpson, in Texas Sept. 24, a family rep assured Us Weekly the split was "amicable." Behind the scenes, however, a source says the couple's elder daughter, 32, was appalled by her father's rush back into the dating world: "Jessica considers it a betrayal." (The engaged singer's parents were married 35 years.)

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The Fashion Star mentor -- who is expecting her second child with Eric Johnson, her fiance of two years -- even skipped her little sister Ashlee Simpson's birthday party for 4-year-old son Bronx Wentz because she couldn't stand to be in the same room as Joe. "One of her girlfriends says it's because she doesn't want to be anywhere near her dad," a source says in the Dec. 10 issue of Us Weekly.

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Even with Jessica absent, "Bat for a Heart" singer Ashlee, 28, and her ex-husband, Fall Out Boy rocker Pete Wentz, 33, hosed a comic-themed fete for their soon at the Coop in L.A.'s Studio City Nov. 20. Jessica's fellow Fashion Star mentor Nicole Richie, 31, and her firstborn, Harlow, 4, also attended.

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"They kids put on costumes and took pictures in a photo booth," a source says of Bronx's party. "It was sweet!"

Jessica, meanwhile, is gearing up for the arrival of baby No. 2. "Jessica loves being a mom," says an insider. "She is really overjoyed."

This article originally appeared on Jessica Simpson Skipped Nephew Bronx's 4th Birthday Party to Avoid Dad Joe