system
A chat on subreddit /r/me_irl
human
A jeweler can identify a lab grown diamond.  So no
gpt
The process leaves artifacts. One leaves tiny flecks of metal behind that are visible under magnification, and there is another used that results in them being slightly flurescent under UV light. But new methods are being developed and are closely guarded secrets. It takes time to determine what artifacts if any are left behind when new ones come out