The Oscar-winning actor - who has been married to wife Shakira for 35 years - believes having your own space is vital to wedded bliss.
He said: "The secret to a happy marriage is separate bathrooms. That's essential. Whenever we stay in a hotel we always get two bedrooms just so we can have an extra bathroom.
"It's vital to have your own space so you aren't constantly in each other's pockets."
Caine met his model wife after seeing her in an advert for Maxwell House coffee and asked his agent to track her down.
The Sleuth star recalled: "Quite simply she was the most beautiful woman I had ever seen. Once I laid eyes on her, that was that."
The couple have a daughter, Natasha.
Caine also has another daughter, Dominique, from his first marriage to actress Patricia Haines.
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