Bachchan, 73, mentioned the "Tamasha" star in a tweet while writing about his film "Ajooba", which also starred Ranbir's father Rishi Kapoor.
"Did you see little Ranbir Kapoor in one of the 'Ajooba' pictures... !! so cute .. 25 years later, huge star!" the National Award-winning actor said.
While Bachchan has worked with Rishi in many films, he and Ranbir have so far shared screen space only in one movie, "Bhootnath Returns", where the 33-year-old actor had a cameo.
On his own work front, Bachchan is currently shooting for Shoojit Sircar's upcoming thriller "Pink", where he is playing the role of a lawyer. The film also stars Taapsee Pannu.