** MORE SPOILERS BELOW **
According to rumours, the battle is between the Lannisters & the Targaryens and happens after Jaime Lannister & his army defeats the Tyrells and takes control over Highgarden. In this scene, they are on their way back to King’s Landing when they are attacked by Dothraki soldiers in an ambush. A dragon is also rumored to be part of the battle. If you want to read more about this scene and other major spoilers, click here.