PHILADELPHIA — Nobody could have predicted the twist ending.

A virtually unknown director from the suburbs of Philadelphia managed to pull off a blockbuster release during a sleepy summer month at just 29 years old. A newcomer called M. Night Shyamalan shocked the world with “The Sixth Sense,” 25 years ago.

Since 1999, the psychological thriller starring Bruce Willis, Haley Joel Osment and Toni Collette has been endlessly dissected, praised and spoofed — from “Scary Movie” to “The Simpsons.” Even this summer it gained traction when Kendrick Lamar referenced it in two of his Drake dis tracks.

Shyamalan just released his 16th feature, “Trap,” on the anniversary of “The Sixth Sense's” Philadelphia premiere. In honor of the film’s 25th anniversary, we take a look back at this unexpected classic.

As a tween, Shyamalan made movies in his parents' backyard in Wynnewood and wrote his own screenplay for a fifth installment of “Friday the 13th.” He went on to study film at NYU. His first two films — the indie “Praying With Anger” (in which he starred) and the flop family comedy “Wide Awake” — gave little indication of his screenwriting chops for horror.

During the day, Shyamalan worked on the screenplay for “Stuart Little,” the adaptation of E.B. White’s kid's novel with Michael J. Fox voicing the cheeky anthropomorphic white mouse. The rest of the time, Shyamalan was writing “The Sixth Sense.” Early drafts focused on a serial killer drama in the vein of “Silence of the Lambs,” but he finally landed on the supernatural story following a child who sees ghosts (Osment) and his therapist (Willis).

He and his wife, Bhavna, flew out to Los Angeles with his spec script, staying at the Four Seasons and praying that the film was good enough to pay for the room. It was: The script provoked a bidding war before Disney picked it up for $3 million.

Aside from its superb cast and unsettling twist ending, “The Sixth Sense” is also beloved for its portrayal of Philadelphia. Thanks to cinematographer Tak Fujimoto, who also filmed Jonathan Demme’s “Philadelphia,” the city's charm blends well with Shyamalan’s sinister mood-making.

Many scenes were filmed in the now-demolished Philadelphia Civic Center in University City, which Osment and his fellow child co-star Mischa Barton were convinced was haunted. (That didn’t stop the adults from partying: The director credits Willis for DJing cast parties and giving him his first hangover.)

Shyamalan worked with Sharon Pinkenson, longtime head of the Greater Philadelphia Film Office, to secure permits to film across South Philly, Society Hill and Center City. That included Old City's St. Augustine Church on North 4th Street, where Osment's character Cole Sear seeks safety and opens up to Willis' Malcolm Crowe. Peirce College served as Cole's school, and he lived with his mom (Toni Collette) in a brick home near Fitler Square at 2302 Saint Albans St.

That leafy street particularly stuck out to Shyamalan when he was scouting locations. “We were actually on a location scout in a van and we were driving by here and I went, 'Stop!' And we jumped out,” he said in an interview in 2019. “Probably the one and only time I ever jumped out of location and was like 'This is it!'”

Shyamalan has mostly maintained that approach throughout his career, with the majority of his films based and filmed in Philadelphia and its surrounding region. (Though his latest, “Trap,” is set in Philly but was shot in Toronto.)

“Philadelphia is home,” Shyamalan told Inquirer film critic Carrie Rickey in 1999. “If you're making movies about people you know and love, you want them set in a place you know and love.”

“The Sixth Sense” joined the list of notable titles shot locally in the '80s and '90s that helped make the case for the city as fertile ground for filming — and by the mid-2000s, the local industry was booming with films like “Marley & Me,” “National Treasure” and “Silver Linings Playbook” making a beeline for Philly.

“It was a very important project for all of us in Philadelphia,” said Pinkenson. “It was a new thing to have movies in Philadelphia, and people were excited.”

On Aug. 2, 1999, Shyamalan joined Willis, Colette, Osment, Donnie Wahlberg and Olivia Williams to walk the red carpet, not in Hollywood but in Center City at the Prince Music Theater (now the Philadelphia Film Center). Boyz II Men’s Shawn Stockman also attended. The buzzy premiere served up cheesesteaks on Chestnut Street. Wahlberg told the Daily News he loved Philly's food scene, including the sandwiches at Nick's Roast Beef, while Williams gushed over the cookies at the Famous Fourth Street Deli.

With the fanfare came the anxiety over how audiences would react. Shyamalan was already writing his next script (“Unbreakable”) and hoping that his $40 million film could at least break even.

“August isn't always the best time for movies. So what I was hearing is we're not sure how this film is going to do,” said Jesse Cute, a marketing executive from Roxborough who worked the premiere when he was fresh out of college. “I don't think anybody, including Hollywood Pictures and Disney, had a clue that it would be the number one film for five weeks, which is unheard of now.”

The film opened on Aug. 6, 1999 — Shyamalan's 29th birthday — and before he and his wife celebrated, they stopped by the Plymouth Meeting movie theater. The director couldn't believe how quickly the shows were selling out. “My initial thought was, 300 people will see the movie — probably more than 'Wide Awake,'” he told The Inquirer. “I thought it might be an anomaly. Was it because I'm from Philly and these are Philadelphia moviegoers?”

It wasn’t just local buzz: The third-act reveal kept audiences coming back to see the Easter eggs they missed, earning success through word-of-mouth. “The Sixth Sense” went on to make a whopping $672 million worldwide ($1.2 billion today). It's still Shyamalan's biggest film to date.

It catapulted Shyamalan (and Philadelphia) into cinematic history, receiving six Oscar nominations, including best director and original screenplay. While Philadelphians may have mixed feelings about their hometown director's movies since then, “The Sixth Sense” has never lost its unshakable, enduring power.