It's nearly impossible to keep a secret in Hollywood, but we dug into our ET vault and discovered some celebrity hookups that might surprise you.
1. Jennifer Aniston & Tate Donovan: The pair dated on Friends and in real life, coupling up for three years before calling it quits in 1998. Tate proved to be quite the lothario in the '90s. Before Jennifer, he was linked to Sandra Bullock. Tate wed TV writer Corinne Kingsbury in 2005 and divorced in 2008. Jennifer famously split from ex-husband Brad Pitt in 2005 after five years of marriage and is now married to actor Justin Theroux.
MORE: ET's Entire Vault of Celeb Flashbacks
2. Sandra Bullock & Matthew McConaughey: The A Time to Kill co-stars dated for a period of time between 1997 and 1998. Sandra eventually found love again with Jesse James, whom she wed in 2005, but the couple later divorced amid rumors of infidelity on Jesse's part. Matthew is now happily married to Camila Alves.
3. Ryan Gosling & Rachel McAdams: The Notebook co-stars reportedly began dating in 2004 before going their separate ways in 2007. Ryan now shares a daughter with his longtime girlfriend Eva Mendes, while Rachel has been rumored to be seeing her True Detective co-star Taylor Kitsch.
4. Julia Roberts & Kiefer Sutherland: In 1991, the then-lovebirds were planning to get married on the Fox Studios lot, but the ceremony was called off just days before the planned nuptials. Today Julia is married to cinematographer Danny Moder, and Kiefer is a two-time divorcee. Before coupling up with Julia, Kiefer had a daughter, actress Sarah Sutherland, with his first wife Camelia Kath. Post-Julia, Kiefer was married to Kelly Winn from 1996 to 2004.
5. Demi Moore & Emilio Estevez: The couple was inseparable from 19985 to 1986, and became engaged before their relationship fizzled. After Emilio, Demi married Bruce Willis in 1987, divorcing in 2000. The actress tried her hand at marriage again in 2005 when she tied the knot with Ashton Kutcher, but they split in 2013. Emilio was married to Paula Abdul between 1992 and 1994, but has been with his current partner, writer Sonja Magdevski, since 2006.
6. Ashton Kutcher & January Jones: Before January's Mad Men fame, Ashton swept her off her feet in 1998 before their split in 2001. After his failed marriage to Demi, Ashton wed Mila Kunis this year. January is reportedly dating her Last Man on Earth co-star Will Forte.
WATCH: FLASHBACK: See Brad Pitt, George Clooney, Julia Roberts & More Before They Were Famous
7. Brad Pitt & Juliette Lewis: These two were reportedly an item from 1989 to 1993 before Brad moved on to Gwyneth Paltrow in 1994. Brad eventually enjoyed five years of married life to Jennifer Aniston before they split in 2005. The Oscar winner has been married to Angelina Jolie for a year, after a two-year engagement. Juliette was married to skateboarder Steve Berra from 1999 to 2003.
Check out more of our throwback interviews in ET: Before They Were Famous, available on newsstands and OnNewsstandsNow.com.