Todd Fisher had long thought about writing a memoir. Then came a double shock: the deaths of his sister Carrie Fisher and mother Debbie Reynolds a day apart in December 2016.

Now, he’s written that book, “My Girls: A Lifetime With Carrie and Debbie” (William Morrow, $27.99). He calls it a “long love letter and thank-you note to the two most pivotal, extraordinary women I’ve ever known.”

Here are five things we learn about this famed, if at times dysfunctional, Hollywood family in “My Girls”:

Eddie Fisher was a world-class (if charming) jerk

Todd Fisher was an infant when Eddie Fisher left his mother for Elizabeth Taylor in a scandal for the ages. When he was a little boy, his father was a “virtual stranger to me,” Todd Fisher writes. He popped in and out of his children’s lives until his death in 2010, often for dubious reasons. When he died, “I didn’t shed a tear,” Fisher writes, because his father “deeply, deeply hurt both my girls.” Still, he thanks him because, “if it weren’t for Eddie Fisher, I wouldn’t exist.”

Unlike his sister, Todd Fisher got along famously with his mother

“My mom was fun and funny and playful and smart and beautiful,” he writes. “It was one of the core facts of my life that she and I adored each other, that we’d had a rare connection from the moment I started growing in her belly.”

He was so crazy about his mother that he did everything he could to try to open a museum for her beloved Hollywood memorabilia collection — it finally was auctioned off for millions. And he defends her questionable taste in men, which led to financial ruin.

After his mother’s third divorce, Fisher writes: “No one worked harder, tried harder, and loved harder than she did. She deserved all the happiness, joy, and security in this world; but she kept getting deceived and robbed blind by men she cared for so much, deeply trusted, and treated with nothing but kindness and respect until the truth of who they really were became unavoidable.”

Carrie Fisher wished she’d never admitted Harrison Ford affair

Fisher writes that his sister came to regret revealing in her 2016 book “The Princess Diarist” that she had an affair with older, married co-star Harrison Ford during the first “Star Wars” movie. Their mother didn’t know of the affair before the book and thought it shouldn’t have been made public, and Carrie Fisher told her: “You’re right. I shouldn’t have told that story.”

As for his bipolar sister’s drug use, Fisher writes that he took her to the emergency room several times after overdoses.

“I didn’t make a big fuss over it,” he writes of one incident in the 1970s. “Drugs and Carrie were old news to me, after all.”

Carrie Fisher died Dec. 27, 2016, after an in-flight medical emergency. Sleep apnea and drugs were factors, according to the Los Angeles County coroner’s report.

Todd Fisher.

Todd Fisher. | Provided photo

Robert Wagner was the love of Debbie Reynolds’ life

At 83, Reynolds had a stroke. She was sometimes confused, and one day she told her son’s wife Cat that actor Robert Wagner was coming the next day to visit her and she wondered if she should tell him something. (She had dated Wagner before Eddie Fisher.)

“I want him to know that I’m in love with him. … I’ve held this in my whole life, and it’s high time I say something, don’t you think?”

Of course, there was no visit from Wagner, but Todd Fisher thought that it’s time “RJ” knows Debbie Reynolds always loved him.

Debbie Reynolds didn’t die of a broken heart

Carrie Fisher and her mother were known for their symbiotic, bickering relationship. But they were extremely close at the end of their lives, so much so that the day after Carrie Fisher died, the mother told Todd Fisher, “I want to be with Carrie.”

But, Fisher writes, there’s more to the story. Reynolds was “completely undone” when she heard her daughter’s body had been taken to the coroner’s office. The family didn’t want an autopsy, and Fisher writes that the idea of his sister “being alone” and dissected by “some stranger was abhorrent to Mom.

“The common theory about Mom’s passing was that, after losing Carrie, Debbie Reynolds died of a broken heart. Take it from the son who was there, who knew her better than anyone else on earth — that’s simply not true. Debbie Reynolds willed herself right off this planet to personally see to it that Carrie would never be alone. That had been her driving force all of Carrie’s life, including having me so that Carrie wouldn’t be an only child, and it continued to be her driving force when Carrie left.”