"In the blink of an eye. Congratulations Gus, you made it," Shweta wrote with one picture, and she captioned another photograph, "Journey wisely".
Amitabh was emotional about the moments.
On his blog, he wrote: "Another (grandchild) several miles away graduates and it's a moment of great pride and joy... The family is all with him and there are frequent messages and pictures flying about.
"But I mean, he was just born the other day and we had all been around his mother at Breach Candy Hospital, and carried him into the world with affection and love... And there he is today, spanking big boy, carnation on his suit lapel, hair flushed back and looking very British... And taller than everyone else in the family.
"Err...almost... still have to see where he measures against Abhishek and me," added the actor, who towers at 6 ft-plus.
Apart from praising Agastya, Amitabh also shared a photograph of a card made by his granddaughter Aaradhya for him.
He dissected the card, and wrote: "She got the French beard and the glasses right... the hair has been through 440 volts, and her own self being loved with the 'U <3 I' is her righteous belief, even before I could genuinely express it myself.. the 'Hey Dood' was an after thought... and the typo... haha."
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)