After Jaime Lannister returns to King's Landing, he goes over with Ser Meryn Trant the placement of the Kingsguard members in defensive positions during Joffrey's wedding, assigning Ser Preston a place close to the wedding feast "primary entertainment".
In the A Song of Ice and Fire novels, Greenfield is a member of Robert Baratheon's Kingsguard. He is noted as the shortest member of the Kingsguard. He accompanied Robert on his boar hunting trip where he was mortally wounded. He pledges allegiance to Joffrey following Robert's death.
Ser Preston is killed in the Riot of King's Landing and replaced by Ser Balon Swann, who has been mentioned in the series but not as part of the Kingsguard. In the series no Kingsguard is shown to be killed by the rioters. Ser Preston is later mentioned as being alive at the time of Joffrey's wedding, meaning he survived the riots in TV continuity.