Credit: Jason Merritt/Getty Images; Kevin Winter/Getty Images Photo: Barry Livingston Will Guest Star on Castle Season 4 Alongside Nathan Fillion

New Nerd Alert! Nathan Fillion (Castle) won’t be the only geek on Castle’s set this fall …

Barry Livingston — best known as adorkable Ernie Thompson on the 1960s sitcom My Three Sons — has been cast as Abe, a man whose run-of-the-mill bank visit turns into a hostage situation.

Other victims? Castle and his mother, Martha Rodgers (Susan Sullivan).

“Castle's trying to help Martha get a loan for her acting school when the bank is taken over," Castle exec Andrew Marlowe explains. "Beckett gets involved from the outside trying to negotiate the safety of all the hostages. Along the way there are lots of twists and turns.”

Although My Three Sons admittedly aired a little before our time, you might recognize Livingston — who’s been all over ABC the last few years — from stints on Desperate Housewives, Grey’s Anatomy, or Eli Stone.

Source: TV Guide