Assault on the Targaryen Fleet

"Give your uncle a kiss!"

- Euron Greyjoy to his niece Yara Greyjoy.

The Siege of the Greyjoy Fleet is an engagement fought during Daenerys Targaryen's invasion of Westeros where the Iron Fleet, commanded by Euron Greyjoy, the King of the Iron Islands, attacks a portion of the Targaryen fleet under the command of his niece, Yara Greyjoy, herself an ally of Daenerys Targaryen.

King Euron sought to capture Ellaria Sand and the Sand Snakes as a gift for Cersei Lannister, whom he seeks to marry to solidify an alliance. Previously, they assassinated her daughter, Myrcella Baratheon, who herself was innocent of any crimes. Nonetheless, Ellaria and the Sand Snakes sought vengeance for the abuses that the Lannisters had committed against Dorne for decades, and killed Myrcella to start a war with Cersei.

Additionally, he sought the deaths of his niece Yara and nephew Theon, who both oppose Euron after he murdered their father and his brother, Balon Greyjoy, and won over the Ironborn at the subsequent Kingsmoot, seizing the Salt Throne of the Iron Islands for himself.

Prelude
Near the end of Robert's Rebellion, Lord Tywin Lannister led the Sack of King's Landing against the Mad King, Aerys II Targaryen, after receiving word of Robert Baratheon's victory at the Battle of the Trident and the death of Prince Rhaegar Targaryen. During the sack, Tywin dispatched the Mountain, Ser Gregor Clegane, to murder Rhaegar's wife, Princess Elia Martell, and her two children, Princess Rhaenys and Prince Aegon. This strained the relationship between the Iron Throne, which had been taken over by Robert Baratheon, and House Martell, the rulers of Dorne.

Years later, Prince Oberyn Martell, the younger brother of Dorne's ruling prince Doran Martell and Elia, arrived at King's Landing and fought against the Mountain at the trial by combat of Tyrion Lannister as his champion, seeking to avenge the death of his sister and her children. However, he was gruesomely killed by the Mountain, his skull crushing death being witnessed by his paramour, Ellaria Sand. Ellaria returned to Dorne and rallied three of the Sand Snakes - Obara, Nymeria, and Tyene - to murder Myrcella Baratheon, the daughter of Cersei Lannister and granddaughter of Tywin, and overthrow Doran and seize power in a coup after Doran refused to go to war with the Lannisters so as to keep his people safe and alive. Under Ellaria, Dorne joined with the Reach, ruled by House Tyrell, in forming an alliance with Daenerys Targaryen, the Mad King's daughter, who sought to take back the Iron Throne and restore her family, House Targaryen, to power.

On the Iron Islands, Balon Greyjoy had declared himself king once more during the War of the Five Kings; previously, he had rebelled against Robert Baratheon during the Greyjoy Rebellion but was swiftly defeated by the Baratheons, Starks, and Lannisters. Eddard Stark had taken his last surviving son Theon Greyjoy as a ward at the end of the rebellion. Balon's campaign to conquer the North during the War of Five Kings failed, however, and he was murdered by his younger brother, Euron Greyjoy, after receiving word from his daughter, Yara Greyjoy, that their last stronghold in the North had fallen.

At the subsequent Kingsmoot, both Yara and Euron claimed the Salt Throne, but Euron ultimately won over the Ironborn and became the new King of the Iron Islands. Realizing their uncle to be a dangerous man, Yara and Theon fled, stealing 100 ships of the Iron Fleet with their loyalists, and sailed to Meereen, where they made a pact with Daenerys Targyaren. Euron previously sought to offer his hand in marriage to Daenerys, but after learning he had been beaten by his nephew and niece, he instead accepted an invitation to King's Landing by Cersei Lannister, who had seized the Iron Throne after the death of her son, King Tommen Baratheon. Euron once more offered his hand in marriage, this time to Cersei, to solidify an alliance between the Lannisters and the Greyjoys, but she declined to marry him. Euron decided to bring Cersei "a priceless gift" to change her mind and vowed not to return to King's Landing until he had that gift for her, much to the distaste of Jaime Lannister.

Daenerys, meanwhile, landed at Dragonstone with her allies. In the chamber of the Painted Table, they discussed their war plans for the Targaryen reconquest. Daenerys ordered Yara, Theon, Ellaria, and the Sand Snakes to go to Dorne with their ships to gather and consolidate their forces.

In the books
In the A Song of Ice and Fire books by George R. R. Martin, no equivalent battle has occurred.