Robert Downey Jr. raises an important Hiddleswift question

Not even Iron Man can resist poking fun at Hiddleswift. 

After Tom Hiddleston finally decided to join Instagram on Tuesday, his co-star and pal Robert Downey Jr. decided to welcome him with a clever post.

The Avengers actor chose to greet his fellow Marvel co-star by mocking his outrageous "I Heart T.S." tank top, a declaration of Hiddleston's apparently true feelings for girlfriend Taylor Swift.

After Hiddleston shared his very first Instagram — a photograph of himself dressed as Marvel's Loki, captioned, "He's back!" — Downey responded with some good old fashioned fun.

The actor shared a photograph of Hiddleston wearing the infamous tank. He cleverly captioned the blurry shot, "Join me in welcoming the biggest T. Stark fan of them all to Instagram!"

We could not be more grateful that Downey's Iron Man character, Tony Stark, and Taylor Swift share the same initials.