LOS ANGELES -- Looks like George Clooney owes Michelle Pfeiffer a lot of money.

The 52-year-old actor -- Hollywood's most determined bachelor, famous for a litany of fleeting loves -- has taken himself off the romantic market, even though he once bet Pfeiffer $100,000 that he'd never marry again.

After dating a string of actresses, models, a cocktail waitress and a former professional wrestler, Clooney recently proposed to 36-year-old international law attorney Amal Alamuddin -- despite repeated protestations that marriage wasn't for him.

"This fascination with my love life is really something," he told the British newspaper The Express earlier this year. "I keep saying I'll never get married again or have children, but people just don't want to believe me."

News of the engagement was announced by the human-rights law firm where Alamuddin works. Doughty Street Chambers said Monday its lawyers and staff "offer their best wishes and congratulations to Ms. Amal Alamuddin ... and Mr. George Clooney on their engagement to be married."

Alamuddin has advised former UN Secretary-General Kofi Annan on Syria, helped ex-Ukrainian Prime Minister Yulia Tymoshenko challenge her imprisonment and represented WikiLeaks founder Julian Assange as he fought extradition to Sweden.

Though they may seem like opposites, the pair, who were first photographed together late last year, have more in common than some might think.

Clooney has shown increasing interest in international affairs and human-rights issues, campaigning for a resolution to the conflict in Darfur and organizing a starry telethon to help Haiti after the 2010 earthquake. He's also hosted fundraisers for President Obama, and recently made headlines for defending the president during an argument with Las Vegas casino mogul Steve Wynn.

So what about Alamuddin made Clooney decide to give up the single life? Specific details are unclear. But she certainly cuts a different swath from his previous public romances. Here's a partial list of loves Clooney left behind:

  • Talia Balsam, married from 1989 to 1993: The 55-year-old actress is now married to actor-director John Slattery of "Mad Men" fame.
  • Kimberly Russell, dated in the mid-1990s: The 49-year-old actress has been married to Michael Bonewitz, who works in film production, since 2000.
  • Krista Allen, dated in the early 2000s: Best known for roles on "Baywatch" and "Days of Our Lives," the 43-year-old Allen met Clooney while making 2002's "Confessions of a Dangerous Mind" and dated him on and off for several years.
  • Lucy Liu, dated in the early 2000s: The 45-year-old "Elementary" star was linked to Clooney in 2000 and photographed kissing him in 2006.
  • Lisa Snowdon, dated in the early 2000s: A British TV personality and fashion model, the 41-year-old Snowdon made headlines for her five-year, on-and-off relationship with Clooney on both sides of the Atlantic.
  • Sarah Larson, dated in 2008: Larson, 34, was a Las Vegas cocktail waitress when Clooney romanced her for nearly a year.
  • Elisabetta Canalis, dated 2009 to 2011: The 35-year-old Italian TV personality went onto become a "Dancing With the Stars" contestant in the United States after she and Clooney ended their two-year romance.
  • Stacy Keibler, dated from 2011 to 2013: A former professional wrestler, Keibler, 34, was Clooney's companion at countless Hollywood events during their two-year relationship. She is now married to entrepreneur Jared Pobre and expecting her first child.