This Is Us fans won't have to wait much longer for an answer to one of the show's central mysteries — why Rebecca (Mandy Moore) and Jack (Milo Ventimiglia) are no longer married. And the answer will come from a surprising source.

On Tuesday's episode, Toby (Chris Sullivan) notices that Kate (Chrissy Metz) is acting strangely and uncovers yet another secret that she's been keeping from him. When she comes clean, viewers will understand why Jack and Rebecca split. The reveal will also definitively change Kate and Toby's relationship.

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In a flashback, we'll also find out how the twins were conceived, and what the heck Miguel (Jon Huertas) was doing there.

(As unlikely as it may seem, both revelations have to do with the family's devotion to the Pittsburgh Steelers.)

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