An insider tells Us Weekly that the pair, who were spotted together two days in a row on July 1 and July 2, arrived at the star-studded bash with a group of friends.
"They were all drinking and enjoying the music," the source reveals. "Ashlee and Evan chatted intimately, whispering in each other's ears and making each other laugh." At one point, the source says that Ross, son of the legendary Motown singer Diana Ross, "put his hands on Ashlee's thighs and sat every close to her. He basically focused his attention only on her."
A second insider added that the pair "definitely looked like more than friends." Notes another eyewitness: "They were totally lovey-dovey and holding hands."
Simpson and Ross were joined by a slew of other celebs at the star-studded party, including Charlize Theron, Mel Gibson, and Woody Harrelson.
As Us exclusively reported on July 2, a source revealed that the pair were just pals ... for now. "Evan and Ashlee have been friends for a really long time, probably 10 years," a source says of the duo. "They know each other from the club scene and have tons of mutual friends."