The rumored couple attended Guy Oseary's party hosted by DeLeón Tequila at Nobu Malibu, and an eyewitness tells E! News that the romance between the singer and Diana Ross' son was very evident.
"They were pretty inseparable," the source tells us, "She was loving the attention she was getting from him."
Simpson and Ross enjoyed the sounds of DJ Ruckus at the star-studded bash, which catered to numerous celeb, including Leonardo DiCaprio, Charlize Theron, Edward Norton and Stacy Keibler (just to name a few).
Guests enjoyed a fabulous dinner by Nobu and children of the stars also had their own special playroom where arts and crafts were provided to make Fourth of July-themed crafts. As the sun set over the Pacific Ocean, guests gathered to watch the fireworks.
The possible new couple were already spotted together twice before in the past week.
Ashlee and Evan were photographed together on Monday as they were strolling the streets of West Hollywood. They were also snapped leaving Teddy's Nightclub in Hollywood and the Sunset Marquis Hotel later that night, and they were seen in Cabo less than two weeks ago.
—Reporting by Marcus Mulick