The actor, who's twice appeared as Barney's (Neil Patrick Harris) father, will be among the many guests appearing in the CBS comedy's final season.

More actors keep sending in their RSVPs for Barney (Neil Patrick Harris) and Robin's (Cobie Smulders) wedding on How I Met Your Mother.

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CBS announced Monday that John Lithgow is the latest prominent guest star of the past to sign on for the upcoming final season, which focuses largely on the long-weekend nuptials of two of the main characters. Lithgow, who appeared twice on the series in 2011, will reprise the role of Barney's do-gooder dad, Jerry Whitaker.

He joins previously announced returning guests such as Wayne Brady and newcomers Sherri Shepherd and Ellie Kemper. And while he has thus far only signed on for one episode of the ninth season, there is room for additional appearances.

"Everyone is heading off to this wedding, and we sort of have this new framework," co-creator Carter Bays recently said of the final season's format, which will see much of the action playing out over the course of just three days. "We want to stress the word 'framework,' because we don't want people to think there [will be] four hours of flower arranging. We're always going to be flashing back and flashing forward. Decades will span over the course of this weekend."

How I Met Your Mother's final season premieres Monday, Sept. 23, with a one-hour episode.