Ashlee Simpson's 'Bat For A Heart' - Listen Now!

Ashlee Simpson and her son Bronx share a smile at his fourth birthday party on Tuesday (November 20) at The Coop in Studio City, Calif.

The 28-year-old singer invited along pals Nicole Richie with daughter Harlow, as well as dad Pete Wentz, and her own parents, who recently filed for divorce, Tina and Joe Simpson.

Ashlee JUST released the full audio of her song “Bat for a Heart,” which has some NSFW lyrics.

Check it out below, and buy it on iTunes now!

FYI: Ashlee is wearing an Anine Bing leather biker jacket.

40+ pictures inside of guests arriving at Ashlee Simpson‘s son Bronx‘s fourth birthday party…