A bombshell for Jerry Lewis fans and other cinephiles was buried in a Los Angeles Times feature story last week — he’s donated his legendarily-unseen Holocaust concentration-camp movie to the Library of Congress.

Now film archivists at the library have exclusively provided details on their prize acquisition to The Post, including why Lewis backed down from his longtime opposition to showing “The Day the Clown Cried,’’ and precisely when and where that will happen. It won’t be until June 2024, and it won’t be easy unless you happen to live in or near Northern Virginia.

Rob Stone, the library’s motion-picture curator, says Lewis, now 89, was approached a few years ago about donating his vast archives. The deal — including “thousands’’ of reels of film — was consummated in June 2014, but the library generally waits until cataloging is complete before making an announcement of an acquisition.

Because Lewis’ donation is so huge, that inventory won’t be done for another “two or three months,’’ he says. But because Stone’s offhand comment to some visitors at a library event has made its way into print, he and Mike Mashon — head of the moving-image section at the library’s Packard Campus for Audio Visual Conservation — agreed to talk about the controversial “The Day the Clown Cried,’’ which was shot in 1972 and has never been released in theaters or on video.

Lewis, who also directed, plays a washed-up German circus clown who is forced by Nazis to lure children to their deaths in concentration-camp gas chambers after he criticizes Hitler. The film got tied up in litigation between Lewis, the film’s producers and its writers, but over the decades Lewis has often given the impression he doesn’t want “The Day the Clown Cried’’ to be released.

One of the few people who has seen even a rough cut of film — comedian and voice-over artist Harry Shearer of “The Simpsons’’ — told Spy Magazine in 1992 that the movie “is so drastically wrong, its pathos and its comedy are so wildly misplaced, that you could not, in your fantasy of what it might be like, improve on what it really is. ‘Oh My God!’ — that’s all you can say.”

Lewis seemed to confirm that assessment in a press conference at the Cannes Film Festival in 2013, the same year that behind-the-scenes footage from a Flemish TV documentary surfaced on YouTube. “It was bad, and it was bad because I lost the magic,’’ he said. “No one will ever see it, because I’m embarrassed at the poor work.”

Why did Lewis (who did not respond to The Post’s requests for an interview) change his mind about letting it be seen — albeit at a point where he may well be dead? “His collection was very comprehensive, and this is part of his career as a writer, director and actor,’’ says Mashon. “He’s not trying to hide ‘The Day the Clown Cried.’ ”

Still, because the film “has a certain notoriety,’’ he says, this is probably why “The Day the Clown Cried’’ is among what Stone terms a “minuscule portion’’ of the Lewis material on which the actor-director has placed “stringent access restrictions.’’

There will be no access at all to the public or even researchers for 10 years after the agreement was signed. “But it’s not like we’re going to stick it in a vault,’’ Stone says. “We can and will do preservation work on the important part of film history.’’

Beginning in June 2024, Mashon says, “The Day the Clown Cried’’ will be available to scholars for viewing in the research center at the 45-acre Packard Campus in Culpeper, Va., and will be shown to the public in the 205-seat theater.

“But that doesn’t mean we’re going to be releasing it on DVD in 10 years,’’ Mashon says. “The copyright and all commercial rights still reside with the Lewis estate.’’ And even if the library wanted to loan a restored print for showing at a museum like MoMA, “We could only do that with permission from his estate.’’