In 55 AC, the elderly Lord Estermont had been wed to a lady of House Tarth. His wife's widowed mother, Larissa Velaryon, chose to stay with her daughter at Greenstone after the wedding. Princess Rhaena Targaryen visited Larissa, her cousin and the first of her favorites, at the castle.
King Robert I Baratheon along with Queen Cersei Lannister and some of the court from King's Landing, including Ser Jaime Lannister of the Kingsguard, spent a fortnight at Greenstone. Robert bedded a widowed Estermont cousin of his and Cersei believes that it was there that she and Jaime conceived their eldest child, Prince Joffrey. Jaime gave the castle the nickname "Greenshit".
A Feast for Crows
After Princess Arianne Martell's failed coup to crown Princess Myrcella Baratheon, Symon Santagar, the Knight of Spottswood, betroths his daughter and heir, Sylva Santagar, to Eldon Estermont, Lord of Greenstone. Ser Symon quickly ships Sylva from Dorne to Greenstone.
A Dance with Dragons
The dank and dismal fortnight Cersei spent at Greenstone, the seat of House Estermont, was the longest of her young life. Jaime dubbed the castle "Greenshit" at first sight, and soon had Cersei doing it too. Elsewise she passed her days watching her royal husband hawk, hunt, and drink with his uncles, and bludgeon various male cousins senseless in Greenshit's yard.—thoughts of Cersei Lannister