Exclusive: Up All Night Welcomes Happy Days Vet Marion Ross -- Find Out Who She's Playing

Up All Night is fast becoming the Happy-est show on television.

TVLine has learned exclusively that — on the heels of Happy Days vet Henry “The Fonz” Winkler being cast as Ava’s fatherMarion Ross has been tapped to guest-star in an upcoming episode of the NBC comedy, playing the tough, doting grandmother of Will Arnett’s Chris.

While Chris is the apple of Gammy’s eye, she can hardly stand Reagan (Christina Applegate), which makes things awkward when her grandson’s better half attempts to convince her to turn over a cherished heirloom.

Up All Night concludes its freshman run in mid-April, making way for the return of the briefly-benched Parks and Recreation on Thursday, April 19.

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