Mathew Knowles' Alleged Baby Mama is FRIENDS With Solange ... But She Didn't Know

7:00 PM PT -- Solange claims she does not know TaQoya, and her rep says the pic is a "random fan photo."

Mathew Knowles' alleged baby mama was tight with Solange Knowles ... but Solange had no idea her friend was banging her dad.

TaQoya Branscomb has sued Mathew, claiming he got her pregnant in 2010 ... around the time Beyonce's mom, Tina Knowles, filed for divorce.

We're told TaQoya met Solange in 2008 through a stylist. They hung out together on multiple occasions in nightclubs and bars in Houston.

Now here's where the plot thickens. We're told Mathew knew his daughter was hanging out with TaQoya. But Solange was in the dark.

Branscomb is asking for a DNA test, a declaration of paternity and child support.