VIDEO : Robert Downey Jr. Jokes Around With Tom Hiddleston on Instagram

Iron Man actor Robert Downey Jr. welcomed Tom Hiddleston to Instagram this week with a picture from his Fourth of July vacation with girlfriend Taylor Swift as well as a hilarious caption to boot. Along with the picture that features Hiddleston in the ocean with his infamous 'I Love T.S." shirt, Downey Jr. wrote, "Join me in welcoming the biggest T.Stark fan of them all to Instagram!" The 35-year-old Hiddleston officially joined the social media platform earlier on Tuesday and posted a debut shot in costume as his Marvel character Loki from the set of Thor: Ragnarok.