New York (AP) -- David Cassidy could sell the heck out of uncertainty.
"I Think I Love You," the smash hit that in 1970 launched the Partridge Family musical group plus the ABC comedy-with-songs show of the same name, found Cassidy center stage delivering such lyrics as "I think I love you, so what am I so afraid of?/ I'm afraid that I'm not sure of a love there is no cure for."
There was no doubt: At 20, Cassidy was the radiant man-boy to help usher young girls (and young boys, for that matter) into the untold mysteries of pubescence, adolescence, romance and rock 'n' roll.
For all that, millions knew they loved him.
Within a few years, those legions of fans would outgrow him, just as Cassidy would outgrow himself, or, at least, what had made him a superstar. His cherubic looks would fade along with his popularity; his laddish proto-Farrah-Fawcett shag would thin. It needn't have shocked him or anybody else; the odds of sustaining that white-hot level of success were no less great than for his having been ignited as a star in the first place. Lightning seldom strikes even once, much less twice.
Cassidy, who announced earlier this year that he had been diagnosed with dementia, died Tuesday surrounded by his family. No further details were immediately available, but publicist JoAnn Geffen said on Saturday that Cassidy was in a Fort Lauderdale, Florida, hospital suffering from organ failure.
"The Partridge Family" aired from 1970-74 and was intended at first as a vehicle for Shirley Jones, the Oscar-winning actress and Cassidy's stepmother. Jones played Shirley Partridge, a widow with five children with whom she forms a popular act that travels on a psychedelic bus. The cast also featured Cassidy as eldest son and family heartthrob Keith Partridge; Susan Dey, later of "L.A. Law" fame, as sibling Laurie Partridge and Danny Bonaduce as sibling Danny Partridge.
"The Partridge Family" never cracked the top 10 in TV ratings, but the recordings under their name, mostly featuring Cassidy, Jones and session players, produced real-life musical hits and made Cassidy a real-life musical superstar. "I Think I Love You" was the Partridges' best-known song, spending three weeks on top of the Billboard chart at a time when other hit singles included James Taylor's "Fire and Rain" and Smokey Robinson and the Miracles' "The Tears of a Clown." The group also reached the top 10 with "I'll Meet You Halfway" and "Doesn't Somebody Want to be Wanted," and Cassidy had a solo hit with "Cherish."
"In two years, David Cassidy has swept hurricane-like into the pre-pubescent lives of millions of American girls," Rolling Stone magazine noted in 1972. "Leaving: six and a half million long-playing albums and singles; 44 television programs; David Cassidy lunch boxes; David Cassidy bubble gum; David Cassidy coloring books and David Cassidy pens; not to mention several millions of teen magazines, wall stickers, love beads, posters and photo albums."
Cassidy's appeal faded after the show went off the air, although he continued to tour, record and act over the next 40 years, his albums including "Romance" and the awkwardly titled "Didn't You Used To Be?" He had a hit with "I Write the Songs" before Barry Manilow's chart-topping version and success overseas with "The Last Kiss," featuring backing vocals from Cassidy admirer George Michael. He made occasional stage and television appearances, including an Emmy-nominated performance on "Police Story."
Even while "The Partridge Family" was still in primetime, Cassidy worried that he was being mistaken for the wholesome character he played. He posed naked for Rolling Stone in 1972, when he confided that he had dropped acid as a teenager and smoked pot in front of the magazine's reporter as he watched an episode of "The Partridge Family" and mocked his own acting.
Cassidy would endure personal and financial troubles. He was married and divorced three times, battled alcoholism, was arrested for drunk driving and in 2015 filed for bankruptcy. Cassidy had two children, musician Beau Cassidy and actress Katie Cassidy, with whom he acknowledged having a distant relationship.
"I wasn't her father. I was her biological father but I didn't raise her," he told People magazine in 2017. "She has a completely different life."
Cassidy himself was estranged from his father. Born in New York City in 1950, he was the son of actors Jack Cassidy and Evelyn Ward and half brother of entertainer Shaun Cassidy. David Cassidy's parents split up when he was 5 and he would long express regret about Jack Cassidy, who soon married Shirley Jones, being mostly absent from his life. David Cassidy stayed with his mother and by the early 1960s had moved to Los Angeles.
Kicked out of high school for truancy, David Cassidy dreamed of becoming an actor and had made appearances on "Bonanza," ''Ironside" and other programs before producers at ABC asked him to audition for "The Partridge Family," unaware that he could sing and intending at first to have him mime songs to someone else's voice. Cassidy, who only learned during tryouts that Jones would play his mother, worried that Keith Partridge would be a "real comedown" from his previous roles.
"I mean, how much could an actor do with a line like, 'Hi, Mom, I'm home from school,' or 'Please pass the milk?'" he wrote in his memoir. "I didn't see how it could do much for me. After all, I wasn't the star of it. Shirley had top billing; I was just one of the kids."
Of course, that wasn't how it worked out.
In the show's musical numbers, he was placed front and center, upstaging Jones, an actress whose beauty and crystalline vocals had graced the movie musicals "Carousel," ''Oklahoma!" and "The Sound of Music." Her voice was buried in the chorus of the other lesser "Partridges."
And while Dey, who was 17 when "The Partridge Family" debuted, soon won a rapt following among the show's boy viewers, she, too, was eclipsed by Cassidy.
It was he who could sell the chaste romanticism of "I woke up this mornin,'/ Went to sleep with you on my mind." For a glorious instant, he made mysteries clearer in the minds of his millions of fans.
AP National Writer Hillel Italie contributed to this report.