Alyson Hannigan Alyson Hannigan

Alyson Hannigan is crashing The McCarthys' Christmas.

The How I Met Your Mother alum has booked a guest-starring role on The McCarthys' holiday-themed Dec. 18 episode, Entertainment Weeklyreports.

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Hannigan will play Pam, the newly-single upstairs tenant of Marjorie (Laurie Metcalf) and Arthur (Jack McGee)  who joins the family for Christmas Eve. She doesn't have any idea what she's in for, however, as the family's annual gift exchange brings out the best and worst in all of them.

The McCarthys airs Thursdays at 9:30/8:30c on CBS.

(Full disclosure: TVGuide.com is owned by CBS.)

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