Towards the end of his life, the great Leonard Bernstein expressed some regrets about not putting more of his time into composing music, as conducting and performing took up so much of his life. He was a gifted composer, but not a prolific one, so fans are inevitably left wanting more.

Which makes it so exciting that a never published, never performed, never even cataloged piece has been discovered. The concert premiere was scheduled for April of 2020. But finally, after all those delays, the world premiere of Leonard Bernstein's “Music for String Quartet” will happen tomorrow night at Tanglewood, thanks to John Perkel, who is the former orchestra librarian for the Boston Symphony Orchestra. He joined Arun Rath on All Things Considered to discuss the discovery. This transcript has been edited for clarity and length.

Arun Rath: I thought Leonard Bernstein's life and work were pretty well-documented. But let me put this to you. You're the former orchestra librarian. How shocking was it to discover a complete work like this that nobody had ever even cataloged?

John Perkel: It was absolutely mind boggling. This happened about 15 years ago. It was told to me by Lisa Benson Pickett, who was the daughter of Stanley Benson, a violinist from the Boston Symphony, who had been close friends with Bernstein in the 1930s. And Stanley was given the music and never performed it — put it in his drawer.

Lisa, the daughter, didn't even know about it until her mother was driving her after Stanley died to a retirement Boston Symphony party at Blantyre. And when she got to Blantyre, she saw me and she told me the story. I didn't even believe it. I mean, I knew she wasn't lying, but it was just so unbelievable.

And I didn't really do anything until 2018 when Bernstein's Centennial was approaching, and I called her to see if she still had the music. She did, and I had this idea to stage the world premiere. I knew I needed permission from Amberson, Bernstein's company. It took a lot of planning and it took them six months to get back to me, but they finally gave me written permission. And here we are.

Rath: Wow. So going back to when this this piece was composed, this was an 18-year-old Leonard Bernstein, right?

Perkel: That's right.

Rath: And so what went on there? He just handed this work over to this violinist and said, what?

Perkel: We don't know why he wrote it, which makes it that much more intriguing. It might have been a composition assignment from Walter Piston, his composition teacher. The first page of each part was a roman numeral one, which suggests to me that other movements were intended to be written and they either never got written or they got lost. I think the former, we will never know.

Rath: Interesting. It's not formally titled a string quartet — it's called “Music for String Quartet.”

Perkel: Exactly right. And Bernstein signed the first page of each part with his standard signature. That, and the fact that his manuscript was easily identifiable, convinced Amberson that it really was by Leonard Bernstein.

Rath: Now I know Leonard Bernstein was famous young, but 18 — I don't think he was the Leonard Bernstein that we knew.

Perkel: No. It was four years before he became a fellow in the first class of the then-called Berkshire Music Center. And from then on, it was all skyrocketing fame, especially in 1943, when he suddenly took over for Bruno Walter, who was ill and conducted a radio broadcast of the New York Philharmonic, and in the next day's New York Times front page were headlines about Bernstein. And from there on in, it was all as we know Leonard Bernstein, the great Leonard Bernstein.

Rath: Wow. Now we have a bit of tape from one of the rehearsals, and we've been given permission to play just a short excerpt of this, because keep in mind that again, it's a rehearsal. Would this be the first time this has ever been broadcast?

Perkel: Absolutely, yes.

Rath: Awesome, well, let's hear a few seconds of this. This is the start of a rehearsal performance of Leonard Bernstein's “Music for String Quartet.”

Rath: I'm a huge Leonard Bernstein fan, so this is super exciting. There are things that I hear, things that sound maybe a little bit like Ives, a little bit like Copland. Is there anything that sounds really Bernstein-y in this yet?

Perkel: Yes, I agree with you and I would throw in Ravel and Gershwin a little bit. But, yet it is still Bernstein-esque if I may use the word. And to me, it foreshadows later greatness. Remember, he was only 18. Think of other composers, except for Mozart and Mendelssohn, and a scattered few, who already were incredible as a composer.

Of course, Bernstein did so much else for music. As a pianist, as a conductor, as a lecturer, as a teacher. That's why I think he's the ultimate 20th century musician all around.

"He's the ultimate 20th century musician all around."
-John Perkel

Rath: Wow. If you can make an objective musical judgment, is this piece interesting and impressive on its own merits? Or is it mainly of interest because it was written by Lenny?

Perkel: That's a great question. So many people have asked me. It's Leonard Bernstein — unknown work never played, never even known about by ninety nine point nine nine percent of the world. And though the quality of any piece is important, the fact that we're doing it and people are getting to hear it in my mind supersedes your question, and I don't mean to be evading the question. I think it has promise, it's a little bit immature. But he was 18. That's my honest opinion.

Rath: Well, it's so exciting, and I think I speak for a lot of people in saying how grateful we are to you for pursuing this and making it happen. John, thank you.

Perkel: Thank you so much, I really appreciate it. I've been obsessed with this for a year and a half.