David Cassidy’s brother proud of his late teen idol sibling

David Cassidy’s younger brother is proud of the late former teen idol.

“David really had the ability to reinvent himself,” Ryan Cassidy, 57, told The Post in an exclusive new interview while discussing his late sibling’s lengthy career.

David Cassidy died in 2017 following a battle with dementia, he was 67 and had been a household name for more than five decades.

For the duration of David’s career, Ryan was on the sidelines watching his star sibling stay vibrant and viable in the notoriously fickle world of showbiz.

“Through the ups and downs of his career, he still managed to stay afloat and find a way to share his music and his talents,” Ryan explained. “I have just nothing but the warmest best thoughts and experiences that I grew up with David.

“He worked in Las Vegas and he carried himself for a long time and he did very well for himself,” Ryan added, referring to his brother’s residency at the MGM Grand hotel in the mid-1990s.

Ryan is the youngest son of Oscar-winning actress Shirley Jones and ’70s television mainstay Jack Cassidy, who were married from 1956 until 1974.

They had three sons, “The Hardy Boys” star Shaun, Patrick and Ryan. David was from Jack’s first marriage to actress Evelyn Ward. Sadly, Jack died in a house fire at 49 in 1976.

Ryan, who built a career behind the camera working on shows such as “E.R.,” “King of Queens” and “N.C.I.S,” has just penned a children’s book that draws upon a unique afternoon from his star-studded childhood.

Entitled “Jimmy Cagney Was My Babysitter,” it recalls the time when his father dropped him off at family friend Jimmy Cagney’s house and the special hours they spent together.

“I have those memories,” Ryan explained. “I cherished them and I kept them in my memory bank for all these years. And I thought I have to somehow share this story with everybody … And there are some messages in it. He was quite a sweet man.”

Ryan said despite Cagney’s tough-guy persona he was a gentle and kind man who loved animals and took a real interest in hearing what Ryan, then about 7, had to say.

“Sometimes these big movie stars, whether it be James Cagney or a movie star today, are not always who we perceived,” he said. “They’re not always who they really are. You know, James Cagney was a gangster actor. He was a dancer.

“But what I learned from who he was that day was that he was a really genuinely soft-spoken, wonderful man that loved animals, that wanted to draw. He was a painter and he was the total antithesis of all the characters that we may remember him from.”

Cagney was best known for gangster movies “White Heat” and “The Public Enemy” and also for his tap dancing skills, which netted him an Oscar in 1942 for the musical “Yankee Doodle Dandy.” He died in 1986 at 86.

Ryan, of course, knows about big movie stars – his mom was cast in the lead of “Oklahoma!” when she was just 21 and went on to have a long career in film and television including “The Partridge Family” which also starred her stepson, David.

He said that it was sometimes “surreal” seeing his mother at home while watching “The Partridge Family.”

“When mom was doing that show, my brothers and I would be sitting around the dinner table watching ‘The Brady Bunch’ or ‘The Partridge Family,’ when she would be walking through the door from working on it all day,” he remembered with a laugh.

“It was fun to watch. And my mother’s values of who she is in real life are not unlike who she is as Mrs. Partridge. And I think that’s one of the things that’s so appealing about her. She sort of became everybody’s mother.

“And she was an amazing mother to my brothers and me and is still this amazing mother. So it’s been, it was a little surreal at times to know that. But I also was able to separate, even as a child, that that was her career.”