Zendaya Coleman & Gabby Douglas -- Star-Studded High School Graduation ... Even Bob Newhart Was There!

The Oak Park High School graduation of 2015 will go down in history as the first and last time Zendaya Coleman, Gabby Douglas and Bob Newhart came together.

The Disney Channel star and the Olympic gymnastics champ were among the graduates Thursday. Newhart matriculated a looooong time ago, but was there for 2 reasons -- his grandson was in the graduating class ... and Grandpa Bob was the commencement speaker.

Big congrats to Zendaya and Gabby -- and also all the non-famous grads!