Cox, who portrayed Monica on the classic sitcom, said on Wednesday that production on the Friends reunion special would have started already.
The Friends reunion special was originally going to premiere alongside the new HBO Max streaming service in May but has been delayed due to the COVID-19 pandemic.
Cox said that she has started to binge watch Friends as she has a terrible memory and doesn't remember everything that happened on the series.
"I remember obviously loving everybody there and having fun and I remember certain times in my life that I was there, but I don't remember episodes," she said.
Kimmel then invited his cousin Anthony, who is a super-fan of the show, to challenge Cox to Friends trivia.
Anthony knew the majority of the answers, answered faster than Cox and defeated her five to zero.
Kimmel has been producing this new version of Jimmy Kimmel Live! from his home due to the COVID-19 pandemic. The late night host and Cox prompted charity Meals on Wheels which delivers meals to seniors.