John Lithgow

One of How I Met Your Mother's mysteries is about to be revealed.

John Lithgow will play Barney Stinson's estranged father, Jerome Whitaker, Cobie Smulders confirmed on TV Guide Network's Hollywood 411.

Smulders joked that she was terrified of Lithgow after his Emmy-winning role as a serial killer on Dexter, but added, "It's really exciting and different for our show. He's such a pioneer."

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Barney (Neil Patrick Harris) previously believed his dad was Bob Barker, apparently a lie told by his promiscuous mother, who's portrayed by Frances Conroy.  Megan Mullally provides the character's voice in flashbacks.

The episode will air at the end of February. How I Met Your Mother airs Mondays at 8/7c on CBS.