|Although this article is based on canonical information, the actual name of this subject is pure conjecture.
The battle at Dragonstone is an engagement during Daenerys Targaryen's war for Westeros when Euron Greyjoy and a portion of the Iron Fleet ambush Daenerys Targaryen's fleet while they are sailing back to Dragonstone from the North.
- "We have won the Great War. Now we will win the last war."
- ―Daenerys Targaryen
The Golden Company, led by Captain Harry Strickland, was ferried across the Narrow Sea from Essos to Westeros on the Iron Fleet by Euron Greyjoy, Cersei's new ally and the self-proclaimed King of the Iron Islands. The living ultimately prevailed, albeit narrowly, over the dead at the Battle of Winterfell with the destruction of the Night King at the hands of Arya Stark, shattering the White Walkers and destroying the wights. With the Great War having been declared won for the living, the survivors refocused their efforts towards the last war: taking the Iron Throne from Cersei and House Lannister.
After holding a massive funeral for the fallen and celebrating their victory at Winterfell, Daenerys, Tyrion, Varys, Grey Worm, Missandei, and the remaining Unsullied marched to White Harbor and set sail to return to Dragonstone while Jon Snow, the armies of the North and the Vale, and the remaining Dothraki marched south on the Kingsroad towards King's Landing.
Tyrion Lannister and Varys discuss the implications of the parentage of Jon Snow, having learned from Sansa Stark, who, alongside Arya Stark, learned straight from Bran Stark with Jon's permission, that he is Aegon Targaryen, the son of Daenerys's brother Rhaegar Targaryen and Lyanna Stark. Daenerys, meanwhile, flies overhead on Drogon with an injured but recovering Rhaegal next to them. All of a sudden, seemingly from out of nowhere, a gigantic scorpion bolt plunges into Rhaegal's chest. Moments later, a second bolt strikes the Rhaegal's wing, quickly followed by a third bolt which rips through the dragon's throat, fatally wounding him. As Rhaegal plunges into the sea, a portion of the Iron Fleet (about 12 ships), armed with massive scorpions, is revealed to have been waiting at Dragonstone with Euron Greyjoy himself at its command. Daenerys is horrified and enraged by Rhaegal's death; screaming in fury, she directs Drogon to attack the fleet, but relents and pulls up as the scorpions fire again. As they fly away to safety, Euron and his men target the Targaryen fleet and fire on the ships, quickly decimating them. After nearly being hit several times by the shots, Tyrion jumps into the water to escape, as well as Varys and Grey Worm.
The survivors of Euron's surprise attack are able to swim ashore to Dragonstone, among them Tyrion, Varys, and Grey Worm, but Missandei is taken captive by Euron, who returns to King's Landing and delivers her as a hostage to Cersei. Daenerys and Drogon also return to Dragonstone. Daenerys wants to march on King's Landing and destroy the city to avenge Rhaegal and save Missandei, but Varys reveals that Cersei has brought the smallfolk into the Red Keep to hold as hostages, knowing that Daenerys and Tyrion do not want to kill innocent civilians.
Word of the ambush reaches Winterfell. Jaime learns of the ambush and Daenerys's plan to march on the capital from Sansa and Brienne. Later at night, Jaime decides to ride south to try to rescue Cersei, believing he has no other choice, leaving Brienne behind at Winterfell. Brienne pleads with Jaime not to go, and tries to convince him he's a more honorable person than his vicious sister, but Jaime reveals several of his past misdeeds that he committed for Cersei.
Daenerys parleys with Cersei outside the gates of King's Landing. Tyrion and Qyburn, who designed the anti-dragon weapons, discuss their opposing queens' terms of surrender; Tyrion tries but fails to appeal to Qyburn's humanity to save thousands of innocent people, and pushes forward to talk with his sister. Tyrion tries to convince Cersei to surrender in order to save her unborn child, appealing to his sister's love for her children, but Cersei does not give in. Cersei then has Gregor Clegane behead Missandei before Daenerys, Tyrion, and Grey Worm. Daenerys angrily walks away from the parley.
The deaths of Rhaegal and Missandei make Daenerys snap, with her starting to believe she can only win Westeros through fear. This plays a key role in her having Drogon raze King's Landing, even after the city surrenders.
In the books
In the A Song of Ice and Fire novels, no equivalent battle has occurred. The TV show has surpassed the timeline of the books, so it is unclear if an equivalent battle will occur.