The pop singer, 29, and the actor, 25, were joined by dozens of friends Saturday to celebrate their upcoming nuptials at a private residence in Toluca Lake, Calif. "What an amazing engagement party with all of our loved ones! We gettin' married," said Ashlee, who posted a picture of herself kissing her future husband on Twitter.
A source tells E! News, "It was small, intimate, just close friends and family." The Ellis Hall Band provided the music.
Ashlee's famous older sister Jessica Simpson also shared a snapshot from the soiree on Instagram. "Celebrating my best friend and sister @missbananahammock @ashleesimpsonofficial. I love her so much!" she wrote.
The couple wore matching ivory and silver looks, with Ashlee modeling a caftan and a feathered headdress and her fiancé sporting a short-sleeved fur coat and diamond earrings. Jessica, who lost an estimated 60-70 pounds via Weight Watchers, showed off her slim shape in a white and silver mini.
It was an extra special event, as it occurred just days before Evan's mother Diana Ross' 70th birthday.
The "Bat for a Heart" singer and the Hunger Games: Mockingjay – Part 1 actor got engaged in January 2014 and could tie the knot any day now. "Honestly, we could go and get married right now, wherever," Evan told E! News a few weeks ago at SXSW in Austin, Texas. "We just want to be married. We're in love. This is the most incredible time I could ever think of in my life and I'm young, but the same time, I've lived a different life than most and I can't think of a happier moment."
Luckily, Diana is helping the couple plan every aspect of their wedding. "She's involved in all levels of my life. She's one of the most incredible mothers ever," said Evan, who next appears in the indie The Wilderness of James. "She's involved in every piece of our wedding [and] engagement party.
This will be the second trip down the aisle for Ashlee, who was wed to Fall Out Boy's Pete Wentz from 2008 to 2011. Together, the amicable exes share custody of 5-year-old son Bronx Mowgli Wentz.
—Reporting by Sara Kitnick