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She's one of the family now!

Just weeks after saying "I do" to Evan Ross, Ashlee Simpson joined her new family, including mother of the groom, Diana Ross, to celebrate the re-opening of her sister-in-law Chudney Ross' Santa Monica children's bookstore, Books and Cookies.

Four of the five Ross children gathered for the grand re-opening, and Simpson brought along son Bronx, 5, from her first marriage to Pete Wentz.

Posting a photo of the family on Instagram, Evan wrote, "The family. Books and cookies. Amazing"

Captioning another snap from the event, Evan wrote, "The family. My sisters #booksandcookies just opened up. Love when are families come together so beautiful."

His sister echoed the feeling.

"It's so important to have my family here. My family is number one," Chudney told Us Weekly at the celebration, also attended by siblings Tracee Ellis Ross and Ross Naess.

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Meanwhile, the family matriarch praised her daughter, telling Us that she has created more than just a bookstore.

"Chudney has created a nurturing environment and a loving environment where learning takes place," Diana told the magazine.

Evan treated his new stepson to a stack of book, including "Goodnight iPad."

"We've always done Goodnight Moon," Simpson told Us. "And there is a new book we just got called Goodnight iPad which is quite funny. He reads every night! And we brought two bags of books of his to donate today."

Simpson tied the knot with Evan August 31 nuptials at his mother's Greenwich, Conn., estate.

"It was probably one of the best parties I've ever been to," sister Tracee told Us Weekly. "It was very beautiful, we had a moment of oh my god when it was raining crazytown, everything got pushed a little bit and then the rain stopped and there was a rainbow for the ceremony. It was amazing. We couldn't have planned that better. I've never danced and giggled more in my life!"

A week ago, Simpson gushed over her new husband.

"This love is so gooood!!!! My husband!" she wrote beside a photo of the two lovebirds.