From A Wiki of Ice and Fire
Tya Lannister, art by Kwnnos.
|Book||A Game of Thrones (mentioned)|
She was the last member of House Lannister to marry a member of House Baratheon, Gowen Baratheon, before the marriage of King Robert I Baratheon and Queen Cersei Lannister. They had one child, a black-haired boy, who died in his infancy.