It is often said that business shouldn't be mixed with pleasure, but since Hollywood doesn't play by the rules, it's not uncommon for celebrities to date each other after meeting through work, be it on set of a movie or behind the scenes at an awards show.

We often hear about power couples like Brad Pitt and Angelina Jolie or Blake Lively and Ryan Reynold, but there are some duos that you probably never knew got together. Here are 15 surprising celebrity pairs who you won't believe were once in love.

1. Jim Carrey and Renee Zellweger

The pair met on the set of their movie Me, Myself & Irene and got engaged in 1999 before calling things off a year later. Rumor has it that Carrey's mental health and Zellweger's rush to get married was the root of their breakup.  

2. Gwyneth Paltrow and Brad Pitt

Prior to his relationships with Jennifer Aniston and Angelina Jolie, Brad Pitt was actually engaged to actress Gwyneth Paltrow. The couple started dating in 1994 after crossing paths on the set of Seven, but things turned sour in 1997 and the engagement was broken off. Pitt once described his proposal to the starlet as "one of the greatest moments" of his life while Paltrow confessed that her ex-fiance was the one that got away.

3. Jon Bon Jovi and Diane Lane

The pair only dated for about 5 months in the 80s, but Lane has no regrets about it as she thinks "every girl should have such a wonderful experience when she's that young."

There isn't much photographic evidence of Bon Jovi and Lane together, but she has "some photos of him packing on tour."

4. Ryan Reynolds and Alanis Morissette

Back in the early 2000s, before his relationship with Scarlett Johansson and marriage to Blake Lively, Reynolds was engaged to fellow Canadian Alanis Morissette. The actor and singer were together for four and a half years before calling it quits in 2007.

5. Danielle Fishel and Lance Bass

Six years before the former NSYNC member came out as gay, he took his then girlfriend, Boy Meets World actress Danielle Fishel to prom. The childhood friends dated for a year before breaking up at the start of the millennium. Fishel told OK! that her and Bass continued to be friends and to this day they "talk via text." She added: "We see each other when we can, and keep each other updated on what's going on. Our lives take us all over the place, so I don't get to see him nearly as often as I'd like, but we stay in touch regularly."

Continue onto the next page for more surprising pairs including Tom Cruise and Cher.

6. Tom Cruise and Cher

Very few people are actually aware of the fact that Tom Cruise and Cher had a short-lived fling. The unlikely couple dated in 1987 when Cruise was only 25 and Cher was 41. Cher ranked a "shy" Cruise as one of her "top five former lovers" and admitted that she was "crazy for him."

7. Drew Barrymore and David Arquette

The duo played brother and sister in Never Been Kissed, but their real life relationship was sizzling. They dated on the low for a while before parting ways. A few years ago David spilled the beans about their relationship in an interview. He said: "[Drew and I] used to date when we were very young kids. Well, not little kids! She's just one of the sweetest, kindest people in Hollywood. She always has been, and she always will be. She's just a lovely, sweet person. We used to run around and just be silly."

8. Lisa Kudrow and Conan O'Brien

The two comedians dated briefly after meeting in an improv class. The two initially hit it off but soon after realized that they "were better as friends" according to Kudrow. "He was really smart, really funny, and he thought I was funny," said Kudrow.

9. Sandra Bullock and Matthew McConaughey

Their on screen chemistry in A Time To Kill led to a real romance between Sandra Bullock and Matthew McConaughey in the mid 90s. Their relationship didn't pan out but there's no bad blood between them and they're still friends.

10. Justin Timberlake and Fergie

Before his precious relationship with Britney Spears, Justin Timberlake dated a few other pop stars including The Black Eyed Peas' Fergie. Apparently Timberlake was into older women and Fergie fit the bill as she was 23 and he was only 16 in 1996.

"Justin and I would go out together and have fun and make out" said the songstress in an interview, "we were never serious. He was Mr. Right Now."

Click on the next page for even more odd celebrity couples.

11. Madonna and Michael Jackson

The pop royals shared a platonic relationship until Madonna made a move on Jackson. She admitted in a recent episode of Carpool Karaoke that she gave the King of Pop a "full French Kiss" but their relationship never turned into a full blown romance.

12. Tyra Banks and Seal

Circa 1996, supermodel Tyra Banks and singer Seal made one public appearance together at the Essence Awards which confirmed rumors about their under-the-radar relationship to be true.  

13. Winona Ryder and Matt Damon

He may not have a tattoo to prove it (looking at you Johnny Depp), but once upon a time in the 90s, Matt Damon and Winona Ryder were an item. The couple met through their friends, Gwyneth Paltrow and Ben Affleck in December 1997 then went public with their relationship at the Harvey Weinstein's pre-Oscar party in March of 1998. They were together for nearly two years but broke up in 2000.

14. Johnny Depp and Jennifer Grey

The pair haven't made any official red carpet appearances together, but they were snapped out and about multiple times. Rumor has it they were even engaged before they ended the relationship after a year.

15. Ashley Olsen and Lance Armstrong

Ashley Olsen and Lance Armstrong may be one of the oddest pairing on the list so we saved it for last. The two were spotted "making out" in a New York City bar back in 2007. There aren't many details as to how they met or how long the relationship lasted, but it wasn't until a year later that Ashley was seen in the arms of another man.

Did any of these couples surprise you? Let us know in the comments!