Ser Duncan the Tall dies at the Tragedy of Summerhall, in 259 AC, alongside King Aegon V and others, but the exact manner of his death has never been fully revealed in canon.

Canon answer: what we know

From the main lore of A Song of Ice and Fire and the in‑world history book The World of Ice and Fire, we’re told that:

  • Duncan rises to become Lord Commander of the Kingsguard under King Aegon V Targaryen.
  • In 259 AC, during the mysterious “tragedy of Summerhall,” Duncan dies along with Aegon V and Prince Duncan Targaryen.
  • The fire at Summerhall is described as a great conflagration that “consumed” the castle, and it is hinted that the Lord Commander’s valor saved some people from dying in the blaze.

So in strict canon:

  • What happens to Ser Duncan the Tall?
    He dies heroically in the great fire at Summerhall; the details are intentionally left vague and are meant to be filled in by future Dunk & Egg stories.

Theories and fandom discussion

Because the text is deliberately fragmentary, fans have spent years speculating about what, exactly, Dunk did in those final moments:

  • A frequently cited fragment from an in‑world letter speaks of “many would have died, but for the valor of the Lord Comman…” which most readers take to mean “Lord Commander Duncan the Tall.”
  • One popular theory: Dunk physically holds up collapsing beams or a wall, buying time for Aerys II and Rhaella (pregnant with Rhaegar) to escape the spreading wildfire, and dies when the structure gives way.
  • Another take is that Aegon V orders Dunk to prioritize saving his heirs (Aerys, Rhaella, and the unborn Rhaegar) over trying to rescue the king himself, and Dunk obeys, dying in the fire after completing that duty.

These ideas are not confirmed in the books, but they fit the known facts: a catastrophic fire linked to dragon‑egg hatching attempts, wildfire, and Dunk’s well‑established tendency to throw himself into danger for others.

Where the story stands “right now”

As of early 2026:

  • The published Dunk & Egg novellas stop long before Summerhall, so we have not yet seen Dunk’s actual death on the page.
  • Interviews and commentary keep hinting that the full Summerhall story—including Dunk’s end—is reserved for future Dunk & Egg installments or related material, but nothing final has been released yet.

So for now, when you ask “what happens to Ser Duncan the Tall,” the solid answer is:

  • He becomes Lord Commander of the Kingsguard,
  • Dies in the Tragedy of Summerhall in 259 AC,
  • Almost certainly dies performing some act of major heroism in the fire,
  • But the precise scene is still an open mystery the series hasn’t shown us yet.

TL;DR:
Ser Duncan the Tall’s confirmed fate is that he dies in the Tragedy of Summerhall in 259 AC, likely saving others from the catastrophic fire there, but the exact details are intentionally unrevealed and remain the subject of fan theories.

Information gathered from public forums or data available on the internet and portrayed here.