G.O.A.T. blood apparently runs thick in the Tom Brady family ... 'cause the greatest quarterback of all time just revealed his 15-year-old son is nearly as big as he is now!!!
The 6-foot-4 Brady shared the eyebrow-raising update in an Instagram post on Thursday afternoon ... showing Jack -- his son with Bridget Moynahan -- is only a couple inches away from Pops now.
"Not Yet Kid!!!" Brady said in a caption on the post. "I'm still here."
The 44-year-old added a bunch of laughing emojis and a few hearts as well.