The singer, 44, announced the arrival of their first child together via Instagram.
But many of her fans are convinced her son has been named after the late George Michael, a close friend of Horner.
“Geri, his second name goes for George Michael?” asked one fan, while another wrote, “Congrats <3 George Michael must be smiling up there in heaven.”
The two were good friends before Michael’s death on Christmas Day last year, with Horner writing at the time, “So so sad, RIP George, a dear friend, the kindest, most generous and talented person.”
Michael’s ex-partner, Kenny Goss, is also godfather to Horner’s 10-year-old daughter, Bluebell.
The former Spice Girl has been keeping her 400k plus social media fans updated throughout her second pregnancy.