King Charles needed a coronation song. He summoned Andrew Lloyd Webber.

His Majesty wanted a song. Or not so much a song as a composition — of a sort fit for, well, a king. For the day of his coronation, in Westminster Abbey, on May 6 in the year of our Lord 2023.

So it came to pass that Lloyd Webber set down a melody to Psalm 98, the one that goes, aptly enough, “O sing to the Lord a new song.” Then he gathered together his flock — “half the kids in my office,” he said — and with them the Lord he madeth a demo; the Lord in this case being Lloyd Webber.

To a Yank’s way of thinking, it is quite the thing for a Broadway composer to turn court composer, to have one’s notes ring out in the storied nave where the royal British line has been consecrated for a thousand years. And hearing them in an Anglican service along with music by the likes of George Handel and Edward Elgar.

Lloyd Webber has a more businesslike attitude about the whole thing. Sitting in an otherwise empty dining room in the Lambs Club on West 44th Street recently — he’s in New York for the opening on Thursday of his latest musical, “Bad Cinderella” — Lloyd Webber talked rather matter-of-factly about the assignment.

“I have written quite a lot of choral music,” he said. “[M]y father was a very distinguished church organist and choirmaster and the choral tradition is not something that is new to me in a way, because it’s been there all my life.”

It’s unfair to conclude that Lloyd Webber is not excited by this opportunity. He’s so even-keeled and obliging in conversation, in an English let’s-keep-our-wits-about-us sort of way, that you can’t really tell how much of a charge he gets out of this. It’s not as if Lloyd Webber is a close confidant of the king or anything — although this is not the composer’s first go-round with Charles III on matters of serious musicianship.

“The great thing about Charles is that he has a great love of really quite a lot of causes that are a little bit unfashionable,” Lloyd Webber said, in a flagrant understatement. “He cares very deeply about all sorts of quite interesting things. I mean, like, three or four years before lockdown, I got a call from him saying could I come around to meet him at Lancaster House quite urgently, because he’d had an idea. What it was that he was worried about was the fact that there wasn’t enough access for young people to go and learn how to play the church organ.”

Likewise, there are quite a few quite interesting things going on in the life of Lloyd Webber, who turns 75 on Wednesday and is in another turnstile moment of his career. The end of the Broadway line approaches for “Phantom,” which opened here a year before the fall of the Berlin Wall and has already logged 13,941 performances. Its last day will be April 16, and Lloyd Webber is not sanguine about it.

“The truth of the matter is ‘Phantom’ does not need to close in New York at all,” Lloyd Webber said, suddenly allowing his pique to surface. Though his company, Really Useful Group, has in the past produced a number of his musicals — and owns six theaters in London’s West End, including the highly prized Theatre Royal Drury Lane — “Phantom” is the purview of producer Cameron Mackintosh. Lloyd Webber claims the marketing of the show had become old hat, and allowed interest to atrophy.

“My boys work in the music business and they said, ‘Dad, you’ve got to wake up to what’s really going on and it’s called, obviously, social media,’” he said, referencing sons Nicholas, 43, Alastair, 30 and William, 29. The proof for him, Lloyd Webber asserted, came after a remix of a “Phantom” song went viral on TikTok on Halloween, and then spurred ticket sales among younger fans. “The young have discovered it, which is why it’s going through the roof,” the composer said, noting that the planned closure of the show had to be postponed until April to accommodate the last-minute surge.

“There was a whole missing generation of ‘Phantom’ people,” he claimed. “And now suddenly the young again, now they’re saying that they want to bring their friends.”

Marc Thibodeau, a spokesman for Mackintosh, said the producer “is thrilled with the absolutely phenomenal response to the closing both from longtime fans coming back one last time, as well as people of all ages who have never seen the show before.” He added the show was “losing money most weeks prior to the closing announcement, and the tremendous response is precisely because theatergoers understand it’s going away.” The extension ends on April 16 because the Shubert Organization “will begin renovations shortly thereafter.”

But maybe now, fans will flock to “Bad Cinderella,” the new show he’s written the music for, with lyrics by David Zippel and a book by Emerald Fennell, who was head writer for Season 2 of the BBC’s “Killing Eve” and played Camilla Parker-Bowles on Netflix’s “The Crown.” The musical is a cheeky pop-styled twist on the fairy tale, with a mischievous Cinderella played by Linedy Genao.

The musical at the Imperial Theatre has had “Bad” added to its title for Broadway, after a start-and-stop premiere run in London ultimately done in by covid disruptions. The irony was Lloyd Webber was way out front in the covid prevention effort in the initial stages of the pandemic, even volunteering in 2020 for the University of Oxford’s preliminary coronavirus vaccine trials. Three years later, the coronavirus is still frustrating his efforts to get his work on a reliable schedule: Over the past few days, emails went out from “Bad Cinderella’s” press team postponing invitations to critics because key cast members were testing positive. (The formal opening night is still set for Thursday, with reviewers invited on Wednesday.)

He’s regretful over what he views as the premature closing of “Cinderella” in London in June 2022, after a positive critical reception. He says he terminated the run because so many actors were out sick that “it was almost the stage managers going on and taking the leading roles.”

“I suppose a commercial producer would have just said ‘Look, what we need to do is just keep going and take the public’s money.’ I can’t do that. You know, I just thought it was wrong.”

As for the future: Lloyd Webber is trying to figure out what his next musical might be, after nearly two dozen of them. It’s not as easy for him to settle on a project as it once was. “I haven’t found the subject that I really want to write yet. Because finding a subject these days for various reasons is much more difficult than it used to be. Because you’re not from that background, or you’re not from that, you know, blah, blah, blah. And I keep thinking to myself, would I have therefore ever written ‘Evita’? Because I’m not Argentine? You know? What is the world coming to?”

The royal-watching world in short order will be hearing from Lloyd Webber, in the form of his three-minute piece for the coronation, alongside new works by classical composers including Roxanna Panufnik, Tarik O’Regan, Roderick Williams and Shirley J. Thompson. After this interview, he was soon to head back to London to help sort out the challenge of how well the music will be heard in the ancient church. He says his spiritual home is Times Square (“If you love musicals, you love Broadway”), but his latest song is written for king and country.

Bad Cinderella, music by Andrew Lloyd Webber, lyrics by David Zippel, book by Emerald Fennell. Directed by Laurence Connor. At Imperial Theatre, 249 W. 45th St., New York. badcinderellabroadway.com.