Kim Kardashian made the announcement Tuesday, posting ... "To our amazing fans -- It is with heavy hearts that we’ve made the difficult decision as a family to say goodbye to Keeping Up with the Kardashians."

She adds, "After what will be 14 years, 20 seasons, hundreds of episodes and numerous spin-off shows, we are beyond grateful to all of you who’ve watched us for all of these years – through the good times, the bad times, the happiness, the tears, and the many relationships and children. We’ll forever cherish the wonderful memories and countless people we’ve met along the way."

Kim goes on to thank EP Ryan Seacrest, E! and countless others.

KKW also says their final season will air in 2021 -- but she doesn't explain why the "First Family" of reality TV is saying farewell to their hit show.

What she does finish with is a lot of gratitude for what the series has brought her entire family. Kim writes, "Without Keeping Up with The Kardashians, I wouldn’t be where I am today. I am so incredibly grateful to everyone who has watched and supported me and my family these past 14 incredible years. This show made us who we are and I will be forever in debt to everyone who played a role in shaping our careers and changing our lives forever."

'KUWTK' has had an incredible run -- 20 seasons is a milestone few TV shows ever hit -- plus it became a pop culture fixture over that time.