Showtime has tapped stage and TV star Christian Borle for a recurring guest star role for the second season of its period drama “Masters of Sex.”

Borle, whose credits include Broadway’s “Spamalot” and “Legally Blonde”  and TV’s “Smash” and “The Sound of Music Live!,” will play Frank (Francis) Masters, the brother of Michael Sheen’s uptight doctor William Masters. He joins an ever-growing cast that includes season two newcomers Betsy Brandt, Sarah Silverman, Keke Palmer, Courtney B. Vance and Rene Auberjonois.

Borle is repped by CAA and Management 360.

Filming on season two of “Masters of Sex” is already underway in Los Angeles and premieres on July 13. Judging by the recently released season two trailer, the upcoming episodes will concentrate on the love triangle between Masters, his wife Libby (Caitlin Fitzgerald) and his research assistant Virginia Johnson (Lizzy Caplan).