He does not hesitate to hit Sansa Stark again and again on order of King Joffrey I. Sansa considers him the worst member of the Kingsguard. Ser Boros survives the riot of King's Landing, when the royal procession is attacked on its return to the Red Keep after seeing Princess Myrcella off to Dorne.
He is arrested and removed from the Kingsguard by Queen Cersei. This is due to his surrender without a fight to Tyrion Lannister's men when they were escorting Prince Tommen to the castle of Rosby.
He is reinstated to the Kingsguard by Lord Tywin Lannister upon his return as Hand of the King, to fill the vacancy left by Sandor Clegane when he deserted. During the trial of Tyrion Lannister for the death of King Joffrey, he recounts the tale of Tyrion beating Joffrey after the riot and the threat against Joffrey's life. After the death of the King Joffrey, the Lord Commander of the Kingsguard, Jaime Lannister, makes Ser Boros the official food taster of the new king, Tommen I, a shameful post for any knight.
Ser Boros remains at the Red Keep. He guards Tommen when Ser Kevan has dinner with Cersei and the King. Ser Kevan thinks Blount feeble, and that tasting food is possibly the only thing he is good for. At the dinner, Ser Boros appears heavier and in poor health. He has a difficult time standing for the duration of the meal, and has to lean on a wall for support.