"I was well into the assignment to do a lavish pictorial tribute to Grace Kelly when I discovered there was a lot I didn't know," the professorial- looking author said.
"I'd heard stories about her sexual exploits - but I couldn't substantiate them," said Spada, a former press aide to Sen. Edward Kennedy and author of the only authorized biography of Robert Redford.
Spada said he had a breakthrough when his research led him to Don Richardson, Kelly's coach at the American Academy of Dramatic Arts in New York and her on-again off-again lover.
"He shattered the myth of Grace Kelly as the demure darling of Hollywood and gave me incredible stories about her wild side," said Spada, who also examined the couple's lengthy correspondence, which lasted until Kelly's death in September 1982.
"This could no longer be the coffeetable book I was asked to do. I convinced my editor at Doubleday that the real story had never been told - this was going to be different than anything ever written about her."
Doubleday gave Spada a six-figure advance and had him totally revamp the book.
"I took a private investigator's course - learning how to sniff out leads and dig out information and ask hard-hitting questions," said Spada, who has penned 11 pictorial books including critically praised best-sellers on Barbra Streisand and Marilyn Monroe. "I felt like Sherlock Holmes."
He spent two years tracking down Kelly's friends, relatives and co-workers in Hollywood, New York, Philadelphia, London and Paris. "The real story was well-hidden," he explains.
When Spada contacted Kelly's sisters, Peggy Conlan and Lizanne LeVine, who live in Philadelphia, the Kelly family lawyer wrote back: "The princely family has not authorized the book." But Spada didn't give up. "I sent them copies of my Streisand book. After six months, they finally agreed to speak to me. It was worth the wait - their interviews were incredibly revealing."
Two other Grace books - Sarah Bradford's Princess Grace and Steven Englund's Grace of Monaco - have been published, but, Spada pointed out, those 1984 publications "were started before she died. Her family and intimate friends talked more frankly after her fatal car accident. And I was armed with information I'd gotten from Richardson."
Judging from an advance copy of Grace, with its plentiful anecdotes from the Philadelphia society girl's allegedly promiscuous past, Doubleday's lawyers were kept busy.
"It's amazing how she was able to maintain her virginal public image," said Spada.
Spada discusses the young actress' alleged antics in New York - an affair and marriage proposal from Aly Khan; an attempted rape by Al Capp during an audition; a stint as mistress to a maitre d' at the Waldorf-Astoria because of his celebrity connections.
Then there were what he calls the "white-gloved" days in Hollywood. ''Gore Vidal told me she was famous for almost always sleeping with her leading men," said Spada. "My research proved him right."
At 22, the "Ice Queen" fell into the arms of her married High Noon co- star, Gary Cooper, who was 28 years older than she, Spada says. He also managed to dig up what he says are details about a 1952 affair with Bing Crosby, her co-star in The Country Girl (1954) and High Society (1956), while Crosby's wife Dixie Lee was dying of cancer.
Kelly's affair with Ray Milland, 45, while they were filming Dial M for Murder (1953) led to marriage discussions, Spada writes, but the Kellys convinced their daughter to drop the married Milland. Spada quotes a friend of Milland's wife as telling him (Spada), "She wore white gloves, but she was no saint."
Spada says he learned that the studios were buying off journalists to keep her image pure, and that when Kelly started dating Crosby again, she was usually chaperoned by one of her sisters.
"She was always seeking her father's approval and never getting it - perhaps that fueled her interest in older men," Spada speculated. According to the author, Grace - a black sheep who had been the least favorite of her father's daughters - remained a disappointment to John B. Kelly Sr. until his death in 1960.
"Bing wanted desperately to marry Grace," said Spada. "But she rejected him. She was the love of his life and he carried a torch for her his entire life."
The 23-year-old star rekindled a prior romance with the married William Holden, who was 11 years older, according to Spada, and they, too, discussed marriage. But their publicized affair threw her father into a fury and drove Grace to the psychiatrist's couch, the author writes.
It was an editor at Paris Match magazine who orchestrated a meeting between the Movie Queen and the eligible Prince of Monaco. What started out as a photo feature led to "the wedding of the century."
But before their vows were exchanged in 1956, the financially strapped Rainier demanded a "huge secret dowry," according to Spada, who also maintains that Rainier arrived at the Kellys' Philadelphia home with his private doctor in tow - "to perform a pre-marital fertility test."
Even after becoming Her Serene Highness at age 26, "life in the palace was no fairy tale," said Spada. "From some of her relatives, employees and friends, I learned that her final years were filled with extreme loneliness and drinking bouts."
Spada's detective work led to stories of how the royal couple had drifted apart during the last 10 years of her life. "Grace was very upset about the widespread rumors of his extramarital affairs, and she spent time in Paris and Hollywood," he says. "Gore Vidal told me she accepted a job on the 20th Century Fox board so she could get away from Monaco four times a year."
From Princess Grace's niece, Grace LeVine, a palace regular, Spada got details of how Princesses Caroline and Stephanie rebelled against their strict upbringing. "Stephanie and Caroline embarrassed the hell out of (their mother)," said Spada. "But ironically, neither Caroline nor Stephanie behaved much worse than Grace at their age."
Prince Rainier? "I tried to interview him, but twice I was turned down. I guess he suspected I knew too much."