Rob Gronkowski's retirement will end THIS SEASON ... so says ex-Patriots TE Jermaine Wiggins, who tells TMZ Sports, "You heard it here first, he's going to be back this year!"
30-year-old Gronk famously hung up his spikes this past spring ... but there haven't been many people who have believed he's truly done with football.
Wiggins -- who's still plugged in with the Patriots -- says count him on the side that thinks Gronk's going to make a comeback .