The 71-year-old took to his blog srbachchan.tumblr.com to share his feelings on the special occasion.
"Abhishek just turned 38. It is obvious cliche to start speaking suddenly of the day and moment he was born and what we were up to, of how he behaved when young, of his growing up, his days then to now, little incidents of nostalgic flavour," Amitabh posted on his blog.
He further added: "Now it is best to be with him as an adult a friend a confidante...a support, a companion...that is best what occurs to me, and shall ever remain."
The two have worked together in "Paa" and "Sarkar Raj".