While Ashlee Simpson and husband Evan Ross are “over the moon” to be expecting baby No. 2, a source tells Life & Style exclusively that sharing their pregnancy news with daughter Jagger was “the best part.”

“Ashlee and Evan have been waiting for this day for a long time,” the insider continues. “And Jagger’s been waiting to become a big sister, too.”

The couple revealed they are having a boy on Thursday, May 14, while hosting a gender reveal party on Instagram. Prior to the news, the 4-year-old made it clear to her parents that she was team girl. “Jagger wants a little sister,” a source previously told Life & Style. “No surprise there.”

The “Pieces of Me” singer, 35, announced her baby news via Instagram on April 30. “We are pregnant and we are so excited to share it with everyone,” she captioned her selfie with Evan, 31, while she held a positive pregnancy test.

The couple started dating in July 2013 and the Hunger Games actor proposed in January 2014. They wed that August at the Greenwich, Connecticut, estate owned by Evan’s mother, R&B legend Diana Ross, and welcomed Jagger in 2015. Ashlee is also mom to her 11-year-old son, Bronx, whom she shares with her ex-husband, Pete Wentz.

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Ashlee and the Fall Out Boy rocker were married from 2008 to 2011. After their divorce, Pete, 40, moved on with model Meagan Camper and they’ve been dating since 2011. The Illinois native and Meagan, 31, welcomed two children of their own: 5-year-old son Saint and 23-month-old daughter Marvel. While raising children with exes can cause tension, the four adults have been able to build an “amazing blended family” for their children, an insider revealed to In Touch.

“Ashlee and Pete’s coparenting routine is pretty solid,” the source added. “Everyone gets along, Pete and Evan and Ashlee and Meagan actually like each other,” the source explained. “All the kids get along pretty great. All the kids genuinely like each other. Now they’ll have a new kid to join in on all the fun.” Pete even “called” Ashlee and Evan to “to offer his congratulations” on their new addition to the family, the insider noted.

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He’s not the only one who is celebrating the couple’s upcoming bundle of joy. “Evan’s mom, Diana, and the rest of his family are super excited,” a source tells L&S. Ashlee’s sister, Jessica Simpson, “knows how much Ashlee wanted another baby with Evan,” the insider adds, “so everyone is celebrating the great news.”