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The character Jack stares into the fire during Sunday's episode of "This is Us."

Warning: Mild spoilers for “This Is Us” follow.

“This Is Us” fans felt true heartbreak Sunday night, as the show finally revealed how beloved father Jack Pearson (Milo Ventimiglia) died.

Pearson’s death has been a longstanding mystery from the show’s beginning. Now in its second season, the mystery is over.

Picking up right after the show’s previous episode, in this episode, the Pearson family find themselves trapped in a house fire. Jack works to bring his family to safety, running across the halls and through large flames to rescue his children. The family escapes the home.

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Then they hear their dog bark from inside the house. Jack runs back in the house, saving the dog and some family memorabilia in the process, according to USA Today.

Jack only seems to have suffered from a burned hand and smoke inhalation. He succumbs to a heart attack at the hospital, however, because of the smoke while his wife, Rebecca (Mandy Moore), is at a vending machine getting candy.

Twitter could not handle Jack’s death.

Moore’s moving performance received a thumbs-up from viewers, too.

No one is ready for what comes next.

But Ventimiglia offered this heartwarming thought: