Celebrity Celebrity Family Celebrity Kids Ashlee Simpson Ross Celebrates Son Bronx's 15th Birthday: 'Thank You for Making Me a Mom' Simpson Ross shares her son with ex Pete Wentz, and is also mom to daughter Jagger and son Ziggy with husband Evan Ross By Hannah Sacks Hannah Sacks Hannah Sacks is a writer/reporter for the Parents team at PEOPLE. She has been working at PEOPLE since May 2023. Her work has previously appeared in The Toy Insider, The Toy Book, The Pop Insider, and Saratoga Living. People Editorial Guidelines Updated on November 21, 2023 01:45PM EST Close Ashlee Simpson and son Bronx. Photo: Ashlee Simpson Ross Instagram Ashlee Simpson Ross' son is growing up. On Monday, the singer, 39, shared a photo of her son Bronx Mowgli to her Instagram Story, taking a minute to celebrate the teenager as he turned 15. Simpson Ross posed for a selfie with her son, who looked up from his phone and popcorn to take a picture with his mom, while in a movie theater. "Happy birthday BRONX," the proud mom wrote across her photo. "Thank you for making me a mom! I can't believe your [sic] 15." Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories. Ashlee Simpson and Ex Pete Wentz's Son Bronx Looks All Grown Up as He Towers Over His Mom in Photo Simpson Ross shares Bronx with ex Pete Wentz. She is also mom to daughter Jagger, 8, and son Ziggy, 3, with husband Evan Ross, 35. At Jagger's birthday in August, the mom of three shared a family photo to her Instagram which included a rare peek at Bronx. This past year, Simpson Ross chatted with Jennifer Hudson on her eponymous talk show about Bronx, sharing that he'd been growing up so quickly. The "Pieces of Me" singer marveled at how her oldest is "so tall." "He's like 5' 9½", he towers over me," said Simpson Ross. "He's really chill, though, so I'm lucky for that." She also noted that Bronx's "voice is deep, he's a young man." She also opened up about a recent mishap that happened when she went out to dinner with her son and husband. "I'm sitting next to Bronx and Evan is on [the other] side, and we're at one of those movies where they offer you wine or something, and they were like, 'Oh sir [to Bronx], would you like something?'" Simpson Ross quickly moved to correct the waiter, saying, "He's not my friend — well he's my friend, but this is my kid, my 14-year-old son."