Andrew "Andy" Diggle, Jr., generally known as A.J. Diggle, is the son of the late Andrew Diggle, Sr. and Carly Diggle, the nephew of John Diggle, and the paternal cousins of Sara Diggle (the pre-Flashpoint timeline) and John Diggle, Jr. (Current timeline)
AJ was born to Carly and Andy Sr as their only child. After his father's faked death AJ got close with his uncle John and is pretty much Carly's whole world seeing as she works to provide a better a better life for him. It's unlikely he's still living in Star City since he and mother have been off screened since Season 2 of Arrow despite being mentioned since then.