Kelli O’Hara, Arian Moayed and Seth Gilliam are among the thesps to have joined the cast of the upcoming production of “King Lear” at Off Broadway’s Public Theater, where they’ll appear opposite Sam Waterston as the title character.O’Hara, known for her Broadway tuner output including “South Pacific” and “The Pajama Game,” will play scheming daughter Regan in the show. Moayed, recently nommed for a Tony for his role in “Bengal Tiger at the Baghdad Zoo,” is cast as the upstanding Edgar while Gilliam (“The Wire”) appears as his jealous half-brother Edmund. Michael McKean and John Douglas Thompson also are on board for the production, to be staged by helmer James Macdonald (“Top Girls,” “Drunk Enough to Say I Love You?”). “Lear” was last seen at the Public in a 2007 revival that starred Kevin Kline. The latest “Lear” will be one of a handful of Bard offerings this season at the Public, the company that also produces the Shakespeare in the Park series every summer. Smaller-scale stagings of “Love’s Labor’s Lost” and “Titus Andronicus” also are on tap. “Lear” begins previews Oct. 18 ahead of a Nov. 8 opening.