By R. J. Donovan
Special to The BIR

Award-winning Broadway star Patrick Cassidy represents one branch of a far-reaching family tree of musical performers.  His Mom is Shirley Jones (he was actually conceived during the filming of “The Music Man”).  His Dad was Jack Cassidy.  His siblings include David Cassidy and Shaun Cassidy.  And his niece is Katie Cassidy of “Gossip Girl” fame.

Although L.A.-born and based, Cassidy fondly considers Boston a home away from home.  In addition to having starred in “Joseph & The Amazing Technicolor Dreamcoat” at The Colonial Theatre, he has performed in Williamstown and Connecticut.  It turns out he’s also a loyal Red Sox fan.

Chatting by phone from his home in California, the happily married father of two spoke about making his Reagle Music Theatre debut on August 5 as Captain von Trapp in “The Sound of Music,” starring opposite Sarah Pfisterer as Maria. (Coincidentally, his Mom once starred at Reagle in “Carousel.”)  Here’s an edited look at our conversation.

BIR: So this is your first time at Reagle Music Theatre. How did it come about?

PC: Well, my Mom had worked for Bob Eagle who runs Reagle and told me how wonderful it was.  I had met Bob, I think, when he came to see my mother and me in “42nd Street” on Broadway.  And he said, you know, you should come work for us sometime. And I said, make me an offer.  And he did.  And I’m very excited about it.

BIR:  I understand that “The Sound of Music” represents a full circle for you.  Wasn’t it your first show?

PC: My very first.  When I was 15 years old, in summer stock, it was my first professional gig.  I got my Equity Card in it.  And I didn’t do it because I wanted to be an actor or musical theater performer. I did it  because I was going to turn 16 that following January and my mother said, the only way you’re going to get a car is you have to pay half of it.  Well, I wasn’t going to make enough money at 31 Flavors where I was currently working.  So she said, how about you come on the road with me.  I’m doing “The Sound of Music” for the summer.  And I was like, well, okay, that sounds like a good gig.  But I gotta be back in time to play football.  So I went on the road . . . I got to play a role and I got the theater bug.  Sarah Jessica Parker was in that production, she played Brigitta. It was pretty monumental, actually.

BIR:  You’ve starred in an impressive list of musicals from “Annie Get Your Gun” and “Aida” to “The Pirates of Penzance.”  You also played The Balladeer in the original New York company of “Assassins,” which took on the controversial topic of Presidential killers.  What was it like to be involved in shaping a musical with Stephen Sondheim?

PC:  Amazing, in the sense that every actor dreams about doing a Stephen Sondheim show. But to originate [a role] is an amazing experience because they build the songs, they build the character, they build the music on you . . . I remember very vividly when we were doing “The Ballad of Booth” and how it was literally a fifth or a third lower than ultimately it came to be.  It was just about [Sondheim] going, no let’s take it higher, let’s take it higher.  And when he found the sound that he was looking for, the best sort of voice for The Balladeer, that became it.

BIR:  At the other end of the spectrum, you mentioned “42nd Street,” which is just a great big, happy, tap-dancing extravaganza.

PC: It was the largest show, in terms of a cast, that I had ever been involved in.  We must have had 48 dancers, something like that.  I was in the show for eight months, and I remember still getting to know people by the seventh and eighth month.

BIR:  And your Mom appeared in it as well.

PC:  It was a wonderful opportunity for my mother and me to make a little Broadway history and become the first mother and son to star in a musical [together]. That had never been done before.  And for her, it was a role reversal as such . . . She hadn’t been on Broadway since she’d done “Maggie Flynn” with my father in 1968 . . . so when they came to me and said are you interested, I said Mom, let’s do this.

BIR:  Entertainment is really the family business for you.  So the obvious question is, is it a blessing or a curse?

PC: I do a one-man show called  “Just Act Normal.”  It’s sort of an autobiographical look at what it’s like growing up in a family where every single person around the dinner table is in show business.  Yet we’re still a family, just like any other family.  The backdrop is that, since the day I was conceived, it was lights, camera, action.  So that becomes normal for you . . . You come to think, well this is what the world does.  It’s just like owning a pizzeria or something.

BIR: That’s the family business.

PC:  And you have a normal life . . . I’m very humbled by what’s happened to us and the success we’ve had. There’s not a day that goes by that I don’t thank God for everything that I’ve got.

BIR: Having performed in Boston in the past, do you have any special memories to share?

PC:  It’s one of my favorite cities in the country . . . When I was doing “Joseph” there, the father of one of the children in the children’s choir had offered me [the chance] to sing the National Anthem at Fenway Park.  Something happened with my schedule and I couldn’t do it.  And the Red Sox are my team!  To this day, I regret that.

BIR: So you follow the Olde Towne Team?

PC: I follow the Red Sox religiously!  It’s funny, I became a fan late in life.  Prior to their winning the World Series, people would say, how could you become a diehard Red Sox fan?  You have to be born into that masochism!  And I said, oh no, no, no.  I became a fan in the late 90’s and I wanted to be on the team.  I wanted to be one of those guys. That was my perspective on life -- being the underdog and coming from behind.  And they sure have.

R. J. Donovan is publisher of OnStageBoston.com.

“The Sound of Music,” from Reagle Music Theatre, Aug. 5 - 14 at Robinson Theatre, 617 Lexington Street .in Waltham. Tickets: 781-891-5600 or reaglemusictheatre.org.