When it comes to the relationship square dance, stars in Hollywood swap partners at lightning speed. We regular folk remember their first loves, their long marriages and their painful breaksups -- especially when we're reminded of them every time the star has a movie coming out. (I'm talking to you, Jennifer Aniston.) But in between those

memorable loves are the forgotten romances that make us giggle. Scroll through and see how many lost loves you remember.

Sandra Bullock had a well-documented breakup with Jesse James, but before that relationship even started, she had some "Crazy, Stupid, Love" with an actor who was so much younger than her that friend Hugh Grant used to call him "the child." Can you guess the guy?

It's Ryan Gosling, who met Bullock on the set of the 2001 movie "Murder by Numbers."

Lucy Liu may just be a notch on this serial bachelor's bedpost at this point, but from Christmas to New Years in 2005, their lips were locked so tight, some thought they might need to be taken to the ER to be surgically separated. Who was the handsome fellow?

It's George Clooney, who also dated Liu briefly in 2002.

January Jones is all sorts of knocked up these days, but when the "Mad Men" star first moved to L.A., she dated a Hollywood star who told her she would never make it as an actress. It's safe to say he's not the father, but do you know who her onetime BF was?

It's Ashton Kutcher, who himself went from model to actor, but didn't think his then-girlfriend could pull off the same transition.

Paula Abdul was a "Straight Up" pop superstar before she reinvented herself as a loony tune on "American Idol," and that kind of fame is rumored to be what ended her relationship with this formerly mullet-ed TV star. So who was the dude?

It's John Stamos, whose "Full House" fame wasn't quite on par with Abdul's rock star status.

Natalie Portman just gave birth to the son she conceived with her "Black Swan" choreographer, but back in the day, she briefly dated a noted musician, who claimed that all hell broke loose in nerd land when he hooked up with Portman. Do you know who this bespectacled man is?

It's Moby, who had to fight off the wrath of "Star Wars" geeks everywhere.

Robin Givens had a famous relationship with boxer Mike Tyson, who almost pounded in the pretty face of this actor when he showed up at her house. But she did date the other guy, who she probably remembers more fondly. Who was her A-List actor boyfriend?

It's Brad Pitt, who almost went 12 rounds with Tyson before taking a tabloid beating with the Jennifer Aniston and Angelia Jolie situation.

Demi Moore was married to Bruce Willis for over a decade and eventually made a man out of Ashton Kutcher. But in 2002, she had a summer fling with this rock star, who Willis allegedly wanted to take "under the bridge" and beat up. Who was the lucky guy?

It's Anthony Kiedis, who Willis thought would be a bad influence on he and Demi's children.

Renee Zellweger dated Jim Carrey and Bradley Cooper, had a four-month marriage to Kenny Chesney and was even linked to John Stamos. But on the set of "Cold Mountain," she chose to keep warm with this popular rock star. Who was he?

It's Jack White, formerly of the indie rock band The White Stripes, who had Zellweger at hello.

Tyra Banks was a young model getting her first big television break when she dated the princely star of the show. He's more of an A-list king these days, and even his kids are following in his all-star footsteps. So who had Tyra smizing back in the day?

It's Will Smith, whose "The Fresh Prince of Bel-Air" character falls for Tyra's sexy tomboy character.

Kristen Bell may be engaged to Dax Shepard, but back in college, the "Forgetting Sarah Marshall" star had a gleeful young actor who couldn't keep his jazz hands off her. Who is the now-famous fellow?

It's "Glee" star Matthew Morrison, who swept a young Bell off her feet.

Fergie's dating life has been super boring since she met actor Josh Duhamel, but once upon a time she was an Untamed Flower -- in her girl pop group -- when she opened for and dated this singer, who quickly told her "Bye, bye, bye." Who was he?

It's Justin Timberlake, who famously moved on to Britney and Cameron and Jessica and Mila and whoever may be next.

Sarah Jessica Parker's first Hollywood love was Robert Downey Jr., and she's been married to Matthew Broderick since 1997, but somewhere in between, Mars attacked and so did love. Sadly, the couple couldn't find the secret to a successful relationship. Who won SJP's heart back in the day?

It's Michael J. Fox, who met SJP on the set of "Mars Attacks!"

Britney Spears was half a pop power couple with Justin Timberlake, but in 2003, just before she became queen of the trailer park with Kevin Federline, Britney linked up with this actor, who has quite the Hollywood dating resume. Can you remember the cad?

It's Colin Farrell, who became a red carpet rebound for Spears.

Hilary Duff is all about hockey these days, being married to NHL star Mike Comrie. But back when she was a child star, she opted for tonsil hockey with this fellow kid actor, on what he called the "worst date ever." Who was this not-so-chivalrous dude?

It's Shia LaBeouf who was once a Duff nightmare before dating Carey Mulligan and scoring some on-set "Transformers" love from Megan Fox.