John Stamos is nothing if not a gentleman.

So if Demi Moore wasn't going to explicitly confirm what happened between them 40 years ago when they were both on General Hospital, then he certainly wasn't going to.

Among the juicy bits in his new memoir, If You Would Have Told Me, Stamos describes the actress—who, like him, appeared on the soap opera between 1982 and 1984—as "a firecracker with a gravelly voice and a big laugh" who was "infinitely more sophisticated and worldly" than he was despite being only nine months older.

The action then fast-forwards four decades: He and Moore are catching up at a party celebrating Jamie Lee Curtis' 2023 Oscar nomination for Everything Everywhere All at Once when their writer friend Ali Adler comes over and "totally fangirls out" over them.

Invoking their General Hospital characters, Stamos writes, Adler asks bluntly, "'Oh my god, Blackie and Jackie! Did you two ever f--k?'"

Now, theoretically she could have been asking about Blackie and Jackie (who did not), but Adler was apparently referring to the actors themselves.

"We both look at each other, wondering what the other will say," Stamos writes. "Demi pauses to think about it. 'I don't know if we slept together. I think we fooled around though.'"

Stamos concludes the story: "I just smile. Then ask if she remembers back in the day when we all went to see Rick Springfield at the Universal Amphitheater."

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John Stamos' memoir details friendship, love, loss and the courage to embrace love once more, and is filled with some of the most memorable names in Hollywood.

He then recalls having to leave the concert after some girls in the audience lost it over seeing their favorite soap stud. Moore is mentioned one more time in the book, Stamos referring  to "my old pal from General Hospital" coming to see a show when he starred in The Best Man on Broadway in 2012.

It isn't every day that calling someone "my old pal" sounds so naughty, but such is the effect here.

Stamos previously threw it back to their 20s in 2010, when he tweeted a General Hospital-era photo of them with the caption, "enjoy 2day-these R the gd old days U're going 2 miss in the years ahead." Moore commented, "hilarious!"

Whatever exactly happened between him and Moore, it at least sounds steamier than Stamos' recollection of getting invited to Heather Locklear's hotel room after meeting the Dynasty star at a car show in 1983 but drunkenly passing out in his own room first—leaving Locklear to think he'd flaked on her.

Many years later, Stamos continues, he and Locklear hosted Dick Clark's New Year's Rockin' Eve together and, once he explained what happened, they had a good laugh about it.

But rest assured, the 60-year-old isn't this coy throughout the book. He told the New York Times ahead of its Oct. 24 release that his intent in writing it was to be "100 percent honest" about his life for the first time.

"In a month, whoever decides to read it, they're going to know a lot," he explained. "I saw a lot of deep, dark stuff. And I thought, 'If I'm not 100 percent honest, then why am I doing this?'"

Among the topics tackled in the 352-page book, featuring a foreword by Curtis ("I have people I talk to every day," Stamos told the Times. "One of them is Jamie"), Stamos details his battle with alcoholism, the painful end of his marriage to Rebecca Romiijn, finding happiness again with Caitlin McHugh, how Lori Loughlin dealt with the college admissions scandal and the sudden death of Bob Saget.

Admittedly, Stamos said, the hardest thing for him to write about was his time on Full House, calling his star-making run on the TGIF staple "a blessing and a curse."

But he went there. Read on for everything he revealed about two of the more enigmatic stars he's ever worked with, Mary-Kate and Ashley Olsen:

As John Stamos reveals in If You Would Have Told Me, the twins were the final ones to be cast in the Full House family.

"The last casting call is for Danny's littlest daughter,” he notes, “Two adorable munchkins, Mary-Kate and Ashley Olsen, are cast in the role of Michelle. They have big blue eyes wide with wonder. As identical twins, they can take turns sharing short takes without spending long hours on the set.”

Little did he know just how influential Michelle Tanner would prove to be.

"I'm thinking they've put a lot of work into casting these kids who are just going to be in the background,” he noted, before praising the series creator, “but I admire Jeff [Franklin] for his attention to detail. Good for him."

It wasn’t always smooth sailing for Uncle Jesse when it came to working with the twins at first, who were just six months old when they were cast in 1987. In fact, one day, the dynamic came to a screeching halt.

"I'm trying to get through a scene, and the cutesy twins are crying their heads off,” he writes, “They'd rather be anywhere in the world other than that set, and I'm right there with them."

And this would lead John to deliver an ultimatum to the show’s crew.

"‘It's either me or them,” the ER alum continues, “’They're not going to work out. They'll ruin this show and my career.'”

But John himself notes, "Be careful what you wish for.”

“When you get your way in Hollywood, there's usually a catch. I send the Olsens and their diaper bags packing, and a new set of perfectly behaved twins are paraded onto the set. They are quiet, calm, and homely as hell. I know, I'm one to talk. For the longest time, the neighbors thought my parents got a pet monkey. But here's the difference: I wasn't trying to be in show business yet.”

Needless to say, John requested that the twins (and the diaper bags) come back to set immediately.  

“’Jeff, could we please bring back the Olsen twins?’ I say sheepishly,” he recalls. “I may have misjudged the situation. It turns out that Jeff didn't allow them to go too far, they were actually waiting backstage."

Not only did John begin to bond with the sisters on-set, but as the You actor revealed, they ultimately had a huge impact on the way he envisioned himself as a dad.

"I'm spending more off-camera time with Mary-Kate and Ashley,” he explains, “I adore them, and they adore me. Writers start developing more Jesse and Michelle stories, which become a highlight of the show. We have it down to a science; Mary-Kate is stronger in the emotional scenes, Ashley scores in the comedic ones."

He adds, "I'm starting to really love the scenes with the Olsen twins. Right away, I know the relationship between Jesse and Michelle is an important one, but as the show develops, the connection grows.”

And so does his outlook on his life.

"I'm young, but I want kids someday,” John, who was around 24 years old when he landed the part, continues, “and these lovely little girls, so bouncy and bright, represent the best versions of future dreams. They allow me to consider fatherhood like a benched baseball catcher in a dugout, watching from afar without having to catch any curveballs.”

As he put it, "I take them to Disneyland, I adore them, give 'em kisses on the tops of their heads, buy them a few crappy souvenirs, and then hand them back to their parents to do the hard work.”

It turns out Mary-Kate and Ashley weren't the only family members to forge a bond with John, as younger sister Elizabeth Olsen would also pop onto the set.

"Their little sister, Lizzy, comes to visit them on the set, and she quickly becomes my new favorite Olsen," he explains, "Not knowing, of course, that one day in the future the two of us would both have places in the Marvel Universe (her Scarlet Witch being a little more prominent than the Iron Man voice I do on Disney Plus's Spidey and His Amazing Friends)."

When the General Hospital alum wed Rebecca Romijn in 1998, most of the Full House family, including the twins, were front and center to witness the nuptials.

“Inside at the reception, there are elegant Amazons from her world, Heidi Klum and Tyra Banks, and Rebecca’s Dutch relatives, each taller than the next, eclipsing the models,” he recalled of the event for the couple, who split in 2004. “The Full House family—Candace [Cameron Bure], Mary-Kate, Ashley, and Lori [Loughlin], Bob [Saget], and Dave [Coulier]—all show up to support me.” 

Seven years after Full House came to an end in 1995, John found himself shifting gears and hit the Broadway stage, starring as the Emcee in the Tony-winning revival of Cabaret in 2002. And by then he notes, the Olsen twins were making waves beyond the TV screen as their budding fashion careers were taking off.

“The Olsen twins are all grown up and have moved to NYC to begin building their multimillion-dollar fashion and entertainment businesses,” he writes, “It’s pretty weird having adult Michelles sitting there in stereo watching me play someone so different from their beloved Uncle Jesse, but they get it. We share a mutual pride for how far we’ve all come.”

John shared that his relationship with costar Bob grew increasingly close over the years, especially after their respective splits. (Bob and ex Sherri Kramer broke up in 1997, the same year John and Rebecca—who divorced in 2004—got engaged.)

“Bob and I are now both single and we’re spending a lot more time together as well,” he recalls, “Our relationship is shifting from being good friends to being the brothers we both wished we had.”

And as patriarch of the family, Bob took his role on-and-off very seriously, making sure the Full House family—both in front of and behind the camera—were included in that tight bond.

"Bob rallies the Full House crew to come hang,” John reveals. “He makes sure we all stay close. He knows how important it will turn out to be. I can't think of one sitcom where the cast is closer than family, supports each other, and spends an embarrassing amount of time together like ours. Bob is the glue."

In fact, John recalls one instance where he made sure at least one of the twins evaded photographers after a hangout.

“In the morning, Bob sneaks one of the Olsen twins down to the beach and into a waiting car to avoid the paparazzi,” he shares, “He still feels like a father figure to the girls, no matter how old or rich they become.”

Despite any bumps in the road that may developed over time, (i.e., when Ashley and Mary-Kate decided to not return for Fuller House), when Bob passed away in January 2022, the costars leaned on each other for endless support in real-life. 

“His death brings a well-deserved tsunami of love, an outpouring from all ages, respect from his peers,” John notes, “What a talent. What a kind, good man. What an icon. These are the accolades he wanted all his life. The irony is, he already had it.”