Patti Davis, actress and youngest daughter of the late President Reagan, gave Prince Harry some sage yet unsolicited advice ahead of the release of his memoir, "Spare."

In an op-ed written for the New York Times, Davis, 70, cautioned the Duke of Sussex to be judicious with his candor.

"My justification in writing a book I now wish I hadn’t written… was very similar to what I understand to be Harry’s reasoning. I wanted to tell the truth, I wanted to set the record straight. Naïvely, I thought if I put my own feelings and my own truth out there for the world to read, my family might also come to understand me better," she wrote.

Davis' book on the Reagan family, "Family Secrets," was published in 1993.

PRINCE HARRY STATES HE WANTS HIS FATHER AND BROTHER 'BACK,' ALLEGES PLANTING OF STORIES IN UPCOMING INTERVIEWS

Prince Harry in a dark suit and tie split Patti Davis smiles in a dark blue shirt and shoulder bag

Patti Davis offered Prince Harry some advice ahead of the release of his new memoir "Spare." (Taylor Hill/David Crotty)

"During the early stages of my father’s Alzheimer’s, when he still had lucid moments, I apologized to him for writing an autobiography many years earlier in which I flung open the gates of our troubled family life," Davis admitted. "He was already talking less at that point, but his eyes told me he understood."

Davis saw a parallel between her decision-making and that of the estranged Prince Harry.

"I thought of that moment when I read that Prince Harry, in his new memoir, wrote about his father, King Charles, getting between his battling sons and saying, ‘Please, boys, don’t make my final years a misery.’ Time is an unpredictable thing…I had the gift of time with my father, which allowed me to apologize, even though a disease hovered between us and clouded our communication. King Charles’s words reveal a man who is aware of his mortality and who would like his offspring to be aware of it as well."

Patti Davis, Paul Grilley, First Lady Nancy Reagan, President Ronald Reagan, daughter-in-law Doria, and son Ron.

Patti Davis, left, was Nancy and Ronald Reagan's only daughter. (Bettmann)

CLICK HERE TO SIGN UP FOR THE ENTERTAINMENT NEWSLETTER

Davis called attention to how there are multiple versions of the truth, and since storylines from Prince Harry's book have been teased ahead of its Jan. 10 availability date, she believes the king and Prince William are entitled to their own version as well.

"People generally don’t respond well to being embarrassed and exposed in public. And in the ensuing years, I’ve learned something about truth: It’s way more complicated than it seems when we’re young. There isn’t just one truth, our truth — the other people who inhabit our story have their truths as well," she wrote.

Prince Harry in his military uniform stands behind brother Prince William at the Queen's vigil

Prince Harry has alleged his older brother attacked him in his book. (Aaron Chown)

In recent days, a portion of Harry's book recounting a physical altercation with William was shared with the public. 

"Prince William has, I’m sure, his own take on the physical fight that Harry has described," Davis offered. "To really understand the dynamic between the brothers, to broaden the story and make it more complete, William’s truth has to be considered as well. Harry has written that, after William hit him, William told Harry to hit him back, which he declined to do. But by writing about the fight, he’s done exactly that."

In hindsight, Davis believes she should never have exposed the innermost secrets of her family.

"Years ago, someone asked me what I would say to my younger self if I could. Without hesitating I answered: ‘That’s easy. I’d have said, "Be quiet."’ Not forever. But until I could stand back and look at things through a wider lens. Until I understood that words have consequences, and they last a really long time. Harry has called William not only his ‘beloved brother’ but his ‘arch nemesis.’ He chose words that cut deep, that leave a scar; perhaps if he had taken time to be quiet, to reflect on the enduring power of his words, he’d have chosen differently."

Patti Davis speaks at the podium at the funeral of her mother Nancy Reagan in Simi Valley, California

Patti Davis wishes she chose to "be quiet" when it came to revealing familial turmoil. (Irfan Khan/Los Angeles Times)

CLICK HERE TO GET THE FOX NEWS APP

"Silence gives you room, it gives you distance, and it lets you look at your experiences more completely, without the temptation to even the score. Sometime in the years ahead, Harry may look back as I did and wish he could unspeak what he has said. I’ve learned something else about truth: Not every truth has to be told to the entire world. People are always going to be curious about famous families, and often the stories from those families can resonate with others, give them insight into their own situations, even transcend time since fame flutters at the edges of eternity. But not everything needs to be shared, a truth that silence can teach. Harry seems to have operated on the dictum that ‘Silence is not an option.’ I would, respectfully, suggest to him that it is," she concluded.