Paris Hilton and Nicole Richie celebrate 20 years of living simply

Paris Hilton and Nicole Richie are celebrating the 20th anniversary of The Simple Life , and the reality TV duo has some surprises in store.

Hilton stopped by Watch What Happens Live with Andy Cohen on Nov. 29 and teased how she planned to commemorate the hit reality show's 20th anniversary.

"Nicole and I have been talking and we have some surprises lined up," she told host Andy Cohen. "I can't believe it's going to be the 20th anniversary. It's crazy."

The "Fish Out of Water" series, which aired from 2003 to 2007, told the story of Hollywood celebrities Hilton and Richie who gave up their glitzy lives in Hollywood for small-town America.

The Simple Life aired for five seasons, each with a different theme, including road trips and internships.

Paris Hilton and Nicole Richie in "The Simple Life." 20th Century Fox Television/Kobal/Shutterstock

Paris celebrates 20th anniversary

Hilton also celebrated the 20th anniversary of The Simple Life on Dec. 3, sharing a gallery of throwback photos of her and Richie on Instagram.

" Happy 20th anniversary to the show that started it all, The Simple Life! " Hilton wrote in the caption. "Working with @NicoleRichie on this series was one of the most special, hilarious, and iconic moments of my life. I'm so lucky to have these wonderful memories!"

"love you forever"

Meanwhile, Richie also marked two decades of the series, sharing some highlights from her and Hilton's simpler lives .

"Twenty years ago we weren't just TV stars... we were songwriters," Richie joked in the caption. “Happy anniversary @parishilton.”

Hilton later mentioned her nickname for Richie on the show, responding: "Love you forever, Bill."

Paris Hilton and Nicole Richie. 20th Century Fox Television/Kobal/Shutterstock

In 2014, Richie appeared on "Watch What Happens Live" and praised her former "Simple Life" costar and said she had "a lot of respect" for Hilton.

"Paris has been in my life since day one," Ritchie said at the time. "A true friend is someone who will always be there for you... We are very good friends and I love her and I love her family."