EXCLUSIVE: Ashlee Simpson Looks Incredible and Healthy After Baby at Her 31st Birthday Party

The Rosses and the Simpsons hit the town together!

Can we please talk about how incredible Ashlee Simpson looks?

The singer celebrated her 31st birthday with husband Evan Ross and several members of the Ross and Simpson families over the weekend, two months after giving birth to the couple's daughter, Jagger Snow. Ashlee has another child, 6-year-old Bronx, with her former husband, Fall Out Boy's Pete Wentz.

WATCH: Evan Ross Is Head Over Heels for Wife Ashlee Simpson Ross and Daughter Jagger Snow: 'I'm So In Love'

Ashlee looked super amazing as she and Evan held hands on their way to the restaurant. An eyewitness tells ET that Evan gets along famously with Ashlee's family, and all night, he was "attentive and a gentleman."

Ashlee's mother, Tina Simpson, showed up for the shindig alongside her fiance, Jon Goldstein, and even reunited with ex-husband Joe Simpson for the special occasion.

WATCH: EXCLUSIVE: Joe Simpson Opens Up About Ashlee's Baby for the First Time: 'Jagger is Precious!'

However, our eyewitness says that things became a little awkward for Ashlee's parents, and that Joe tried to leave quickly.

Also there for Ashlee's big night was Evan's mother, legendary singer Diana Ross, and his sister, Black-ish star Tracee Ellis Ross.

PHOTOS: Stars Share Pics of Their Cute Kids

Missing from the night was Ashlee's sister, Jessica Simpson, although her husband, Eric Johnson, did show up for the get-together.

Evan seems so incredibly in love with Ashlee after their first year of marriage, and the 27-year-old poured out his heart and soul while talking about his wife and baby to ET in July.

WATCH: Ashlee Simpson and Evan Ross Welcome Baby Girl

"I've been wrong a long majority of my life," Evan said about what he's learned since tying the knot. "The biggest thing in this world is in love. I'm so in love. I love my daughter, I love my wife. She's given me the best gift in the world. I'm very lucky."

Evan went heavy on the PDA at his own birthday in August, which he posted to Instagram, writing, "My beautiful wife @ashleesimpsonross. Love her so much!!! #birthdaypartyfun."

PHOTOS: Ashlee Simpson Steals Sister Jessica's Maternity Style

Evan calls being a dad a "beyond life-changing" experience.

"She's the most beautiful thing you could ever think of," the actor gushed about his daughter. "I'm proud to be a dad, and I'm going to make sure she knows she's loved, and that's all I can do."

Watch the video below.