Gianna Martell was the sister of Prince Aryyn Martell and wife of King Harys Baratheon. She died giving birth to their own son, Rickon Baratheon. There were rumors concerning her fidelity to her husband, the mention of which started the Bolton Uprising of 490AL.
"My aunt was a strong and passionate woman. My father still grieves her passing as if she left us yesterday." - Sarella Martell
I'm sure you haven't forgotten Gianna? Would you want to see a lady of Tyrell acting as the mother for a Prince of Dorne?" - Gylen Hightower
"The eye was a series of collapsible and connected brass tubes, Myrish made and finely so. It had been a gift from another queen, the long-legged and bronze skinned Gianna of Dorne, upon Aemon's appointment to the Small Council. Bound in leather and twine, it awaited him atop the desk in the solar that the Stormlander would eventually find himself spending more time in than any ship." - Blood and Whispers