Robert Downey Jr. mocks Tom Hiddleston's Taylor Swift tee on Instagram

Robert Downey Jr. welcomed his The Avengers pal Tom Hiddleston to Instagram with a jab at his now infamous Taylor Swift vest.

The 51-year-old actor star plays Tony Stark in the Marvel Universe movies, opposite Hiddleston, who plays his enemy Loki.

After the Thor star joined Instagram on Tuesday (09Aug16), posting a picture of himself in costume as Loki along with the caption "He's back!", Downey Jr. was quick to ask his 11 million followers to welcome the British actor, who is dating Shake It Off singer Taylor.

Sharing a cringeworthy photo of The Night Manager star wearing a white tank top with “I (Heart) T.S.” emblazoned on it, a photo which was taken during Taylor‘s Fourth of July weekend party at her Rhode Island, New York home, Downey Jr. wrote: "Join me in welcoming the biggest T. Stark fan of them all to Instagram! @twhiddleston”.

As yet Hiddleston has not responded to the post, but he has, as a result of Downey Jr.'s post, amassed a few thousand more followers.

The actors, who appeared together in the movie The Avengers are both at work on upcoming films in the universe – Hiddleston is busy finishing Thor: Ragnorak and Downey Jr. is filming Spider-Man: Homecoming.

Hiddleston became a household name when he started dating Swift in June (16), and the pair's relationship continues to hit headlines on a daily basis.

Coping with the new level of fame is a difficult one for Tom, but he recently insisted that as long as he remains "authentic" in every aspect of his life, then he will be happy.

"It comes down to being authentic," Tom told People.com at Comic-Con.. "Everything you do you have to make sure you truly believe in it and as long as you know that, it doesn't matter what anyone else says about it because the nature of being a public figure is that everyone will have an opinion about anything you do, and as long as you know why you’ve done something and you've committed to it with authenticity then you're okay."