Rachel Weisz laughed as talked about “Youth,” the new film (opening Friday) in which she plays Michael Caine’s daughter.

“Talk about an intriguing way to meet someone,” said the Oscar winner. “Michael and I had never really met, except for perhaps a quick handshake somewhere or other. … So here I am, supposed to play his daughter. We don’t know each other really at all. It’s 3 o’clock in the morning. We’re at this amazing hotel in the Swiss Alps. And I have to berate him in the spa!

“Talk about an acting challenge!” said Weisz with a big chuckle. Yet, she went on to say that she and the legendary actor instantly clicked. “Michael Caine is so full of life and joy and curiosity. He’s very unpretentious. He’s met everyone in the world you’ve ever heard of. He has stories for days and is a wonderful raconteur.

“It was very easy to love him and develop a very dependent relationship with him, which was good — because that’s the nature of my character’s relationship with Michael’s character.”

In the film, directed by Paolo Sorrentino (“The Great Beauty”), Caine’s world-famous conductor Fred Ballinger is a self-centered maestro who has retired. Weisz’s Lena has completely devoted her life to working as her father’s assistant and manager — to the point where it has seriously hurt her marriage.

A key subplot of the film is a request from Queen Elizabeth II for Ballinger to give a royal command performance of “Simple Songs,” his most famous composition (which just happens to be Prince Philip’s favorite music) on the occasion of the monarch’s husband’s birthday. Ballinger’s ongoing refusal to comply with this seemingly easy and flattering royal request is an ongoing humorous theme here.

Of course, being in a film titled “Youth” made Weisz ponder that issue and its fast-moving demise.

“Ironically, my Lena character is still too stuck in her youth. She’s a grown woman, but she never has really grown up and is still acting like the little girl around her father — even though they have worked together on his career for ages. … She simply needs to grow up, become an adult, find her own life and leave the nest,” said Weisz.

Adding to that interpretation, the actress stressed Caine’s own ongoing youthfulness, even in his 80s, but noted, “Youth is over in a minute, when you think about it. When does youth — real youth — leave us? Is it gone at 20? At 25? You don’t know what it is when it happens to you — and then it’s gone. Youth in calendar or clock terms is fleeting.

“Yet this film is about an 82-year-old man who suddenly has a future ahead of him,” added Weisz. “By the end of the film you see that and it leaves you with a sense of optimism and happiness, and that’s something I really treasure about the movie.”