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How I Met Your Dad - Lyndsy Fonseca gets Lead Role *Rumor declined by Craig Thomas*

Craig Thomas was asked about the cast for the spin-off at TCA Press Tour, and he said that no one has been cast yet.

Has anyone been cast in the spin-off pilot?
Not yet. “We’re meeting people but no one is cast yet.”

Tassler also revealed that How I Met Your Father, the spinoff of How I Met Your Mother, was pitched to her by the show's creators Craig Thomas and Carter Bays (not the other way around). And the new series, starring Lindsay Fonseca, will closely follow the original HIMYM structure.

"Craig and Carter really broke new ground in terms of developing a new form of comedy and a new mythology and they wanted to keep that going," Tassler explains. "Obviously they're tweaking it somewhat but they just came in with a great pitch, great characters, much like how they did with How I Met Your Mother. In this regard, it is a spinoff. It is Carter and Craig and they are bringing in Emily Spivey, but the way the show is structured and the way the story is told, the way the characters will come to learn about the dad it does follow in form like How I Met Your Mother."