There are precious few cinematic romances that can hold a candle to Rick Blaine and Ilsa Lund in 1942's "Casablanca." It's a relationship that rekindles after heartbreak and is filled to the brim with complications far beyond the usual romantic drama scope. When Ilsa re-enters Rick's life, he's a bit bitter after being left flat with little more than a Dear John letter. He resents being hurt and has lived his life determined to wall off his emotions so that never happens again.

To further complicate things, Ilsa happens to be traveling with her husband, a resistance leader named Victor Lazlo (Paul Henreid), who was believed to have been killed by the Nazis but is very much alive and still fighting the good fight. But Rick and Ilsa's love is deep and real and the two can't help but fall back to their old emotions around each other, even as the noose slowly tightens and they find themselves more and more likely never to make it out of "Casablanca" alive.

Humphrey Bogart and Ingrid Bergman were the personifications of lovestruck individuals, their characters madly and deeply intoxicated with each other and willing to do just about anything to keep that feeling going. The funny thing is, though, that Bogart and Bergman's chemistry only ever existed in front of the camera. The second "cut" was called, all pretense was dropped and none of their character's feelings ever infiltrated their real lives. Like, at all.

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Sure, they're actors pretending to be in love and that's kind of their job, but movie history is filled with co-stars legitimately falling in love. Paul Newman and Joanne Woodward, John Cassavetes and Gena Rowlands, Tom Hanks and Rita Wilson, and Ryan Reynolds and Blake Lively are all examples of how that on-screen chemistry can translate into real life.

According to Stefan Kanfer's 2010 book "Tough Without a Gun: Humphrey Bogart, Men In Movies, and Why It Matters," Bogart was going through a lot of private life drama during the making of "Casablanca," including a tumultuous relationship with his then-wife Mayo Methot, who, it should be noted, he met while they were making a movie together in 1938. Methot was drinking heavily at the time and would accuse Bogart of having an affair with Bergman, which didn't do much to help Bogart's feelings for his costar knowing that her mere presence in his work life was making his personal life a living hell.

Bogart was no angel, though. He'd go on to cheat on Methot with Lauren Bacall just a couple of years after "Casablanca" (another legendary Hollywood example of co-stars falling in love). Methot would later divorce Bogart in 1945 after being diagnosed with paranoid schizophrenia, and because, you know, Bogart actually was messing around on her. Tragically, her depression and alcoholism would spiral and she died in 1951 at the age of 47.

Ingrid Bergman might have had more to do with nothing happening between her and her leading man than Bogart, truth be told. She reportedly never found herself attracted to Bogart off-screen, having said "I kissed him, but I never knew him."

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She also had no spark with her onscreen husband, Paul Henreid, who played Victor Laszlo, the resistance hero and concentration camp escapee who was a vital figure in Europe's fight against the Nazis. That one is a little easier to believe from a cinephile perspective. They're both great actors perfectly cast in their roles, but I never bought them as being madly in love. Ilsa respects her husband, but the fire that the character has is for Rick, which is what makes that love triangle so intriguing.

It should be noted that Bergman was also married (to Petter Lindstrom) when she made "Casablanca," so even if she did feel a spark with either of her on-screen romantic partners she likely wouldn't have acted on it.

Also, despite being thought of as one of the best movies of all time now, most involved with making "Casablanca" thought it was going to be a disaster. None of the actors liked the script and according to actress Geraldine Fitzgerald, the only time Bogart and Bergman really talked off-camera was when they were going over plans to try to get out of their contracts and walk off the movie.

But that's the magic of the movies, is it not? Everybody gets together and for a small sliver of time as film rolls through that camera, they get to pretend to be other people with other passions and life goals. Sometimes actors not getting along can't help but show through in their performances, but sometimes you get one of the most touching on-screen romances ever captured between two people who could barely stand to be in the same room with each other.

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