In his latest action movie “Memory,” opening April 29, Liam Neeson plays a deadly assassin facing his toughest battle: the onset of Alzheimer’s.

While his character copes with his cognitive impairment as a precision hitman, the 69-year-old star has had Bruce Willis on his mind since his fellow action flick staple, suffering from aphasia, recently retired from acting.

“My heart goes out to him. I think about him every day,” Neeson told The Post, noting that aphasia — which affects the ability to express and understand language — is especially cruel for an actor such as Willis. “It’s particularly poignant, isn’t it? I wish him all the best.”

But even as the Irish icon gets ready to turn 70 in June, Neeson has no plans on slowing down. In fact, he’s refuted reports that he’s retiring from action movies.

“That was a joke,” he said. “That was at the Toronto Film Festival a few years ago … One of the Hollywood Foreign Press said, ‘Liam, what is it with you and these action moves?’ I said, ‘I was stubborn … [but] I’ve had enough of action movies.’ But I meant it as a joke.”

Still, playing Alex Lewis in “Memory” — which costars Guy Pearce and Monica Bellucci — made Neeson confront the harsh realities that some face as they get older, including loss of mental faculties. In fact, this notoriously tough guy admits to having a fear of Alzheimer’s. 

“It has crossed my mind a few times, especially when you can’t remember a name of an actor I worked with two or three years ago,” he said. “That bugs me. But maybe we all suffer that.

“In doing some research for this, I watched some very traumatic documentaries on the affliction of Alzheimer’s and dementia, and read some books on it of course. And I have a friend in Ireland, who is older than me, [who] has very definite early stages of dementia, which is traumatic to see … It is a horrible affliction. It really is.”

And, for an actor, remembering lines is perhaps the most important tool of the trade. “I know several actors in London … who have lost the ability to learn lines,” said Neeson.  “They just can’t learn the material. And these are actors who have given extraordinary performances on stage and on film and television.”

One thing that Neeson certainly hasn’t forgotten, though, is how to kick ass onscreen. He’s been doing it ever since he got the part of former CIA operative Bryan Mills in 2009’s “Taken” thanks to a fortuitous meeting with director Luc Besson at the Shanghai Film Festival.

“I approached him and said, ‘As a kid, I was an amateur boxer, and I’d love to be in a film where I have to beat up some guys or get beaten up,’” said Neeson. “They eventually offered ‘Taken’ to me, and I thought, ‘This is great. I get to be in Paris for three months, and we’re going to be working … with these stunt guys, fight choreographers and stuff. And then it will go straight to video.’”

But the sleeper box-office success of “Taken” led to two sequels (in 2012 and 2015) and turned Neeson into a bonafide action star. Now, though, he’d like to flip the script and do a romantic comedy. “I’d love to,” he said. “Yeah, that would be cool.”

Of course, Neeson co-starred in the beloved rom-com “Love Actually” in 2003, and the film still holds a special place in his heart. “You know, sometimes I’m flicking through channels at 2 o’clock in the morning, ‘Love Actually’ starts, and … you hear Hugh Grant talking about the last messages from people [in the planes that hit] the Twin Towers. And all the messages were messages of love. I defy anyone to switch channels when they hear that. I really do.”

In 2009, Neeson’s real-life romance with actress wife Natasha Richardson came to a tragic end when she died from a brain injury incurred in a skiing accident. And, 13 years later, the widower doesn’t believe he’ll ever get married again. “No, I think I’m gonna be on my own,” he said, wistfully.

No doubt keeping Richardson’s memory alive, Neeson will be celebrating with the couple’s two sons — Michéal, 26, and Daniel, 25 — when he turns 70 on June 7. “And,” he added, “if one person says to me, ‘Liam, it’s just a number,’ that’ll be it!”