"#ThrowbackThursday," Kim captioned the vintage photo of the girls looking fresh-faced. "@nicolerichie and I being oh so cool at 13 years old."
Nicole, 32, retweeted the picture, adding her own comment "Brace Yourselves!" in reference to the train track braces on her teeth.
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The picture, which shows the teenagers both wearing white tops and giving the camera the thumbs up, quickly garnered over 480,000 likes on Instagram.
Nicole found fame in 2005 when she starred in reality TV show The Simple Life with Paris Hilton, who went to school with Kim.
Four years later, in 2007, 33-year-old Kim and her famous family hit television screens on Keeping Up With The Kardashians.
Kim and Nicole with Joel Madden and Kelly Osbourne
A lot has changed for both Nicole and Kim in the last 20 years and both women now have youngsters of their own.
Nicole, who married Good Charlotte rocker Joel Madden in 2010, is mother to five-year-old daughter Harlow and four-year-old Sparrow while Kim became a mother for the first time in 2013 when she and her now fiancé Kanye West welcomed baby North.