The child, who is currently living with the mother in Minnesota, is carrying her father's last name on her birth certificate "Peterson."
On the day that Peterson's 2-year-old son Ty died, the mother of Peterson's fourth child posted an emotional message on her Facebook page about the situation.
"Today has been a long finding out my [daughter's] brother passed away and knowing that she never even got to to meet him."
According to sources, Peterson first met the mother of his fourth child while she was serving him in the VIP section at a club called Seven -- a steakhouse, sushi joint and ultralounge all wrapped up in one. It's unclear if the Peterson was involved in the child's life, but the mother recently a photo showing the child wearing all Minnesota Vikings gear.