The 51-year-old "Iron Man" actor wasted no time teasing his "Avengers" co-star by re-posting a blurry paparazzi photo from Hiddleston's now-infamous Rhode Island outing, in which he is wearing 'I love TS' T-shirt.
"Join me in welcoming the biggest T. Stark fan of them all to Instagram," Robert quipped.
Hiddleston used his first Instagram post to share a picture of himself from the "Thor: Ragnarok" set.
Loki's long black hair and a glimpse of his battle armour and robe are all on show in the new image.