See a cute picture of Ashlee Simpson's boyfriend Evan Ross holding hands with her son Bronx, 4. Credit: ashlee evan and bronx

It looks like Evan Ross has won the affection of Ashlee Simpson -- and her son Bronx. The threesome, all wearing printed black T-shirts, looked like a happy family as they held hands together while leaving a house party in Venice Beach, Calif. on Sunday, Aug. 4.

Ross, 24, held onto one of Bronx's hands while mom Simpson, 28, grabbed the other. The "Bat for a Heart" singer told Us Weekly at the launch of Jessica Simpson Fall 2013 Collection on July 31 that Bronx's personal style is "rock and roll and rebel, but really recently he's just into basketball shorts." (Simpson shares custody of her son with ex-husband Pete Wentz.)

Simpson was first spotted in public with Diana Ross' son in early July, and attended their first event as a couple in NYC on July 30. A source confirmed to Us that the longtime friends are dating. "It helps that they were friends first. They have a long bond," the insider explained. "They already know each other really well."

"Evan and Ashlee have been friends for a really long time, probably ten years," another source told Us. "They know each other from the club scene and have tons of mutual friends."

Simpson's last serious relationship was with Boardwalk Empire actor Vincent Piazza. The couple called it quits in November 2012 after a year and a half of dating. "There was no bad blood and no third party involved. It was honestly just a long distance relationship and it became too hard to make it work," an insider explained of the split at the time. "Nobody is to blame. Just the distance."