Tom Hiddleston finally joined Instagram yesterday and fans couldn't be happier. But one person who really couldn't wait to welcome Hiddleston to the photo sharing site was his Marvel co-star Robert Downey Jr, who had a special joke all ready for his pal.

Posting a picture of the actor wearing his infamous ‘I (heart) T.S.’ tank top from his girlfriend Taylor Swift’s Fourth of July party, Downey Jr wrote: ‘Join me in welcoming the biggest T. Stark fan of them all to Instagram! @twhiddleston’.

More: Is Taylor Swift Costing Tom Hiddleston His Work?

Fans were quick to react to Downey Jr’s loving jab, with one commenting ‘You are the master of making epic jokes! @robertdowneyjr.’ and another adding, ‘I love u Rob Im crying’. Meanwhile, Hiddleston made his Instagram debut with a pic of himself as Loki from the set of Thor: Ragnarok, simply captioned ‘He's back!’.

After weeks of Hiddleston and Swift being pictured all over the world together, the couple have been laying low in recent weeks and haven't been seen together in 11 days. But according to The Sun, all is still good with Hiddleswift.

More: Tom Hiddleston Named 'Rear Of The Year' For That Scene In 'The Night Manager'

“Tom and Taylor are 100 per cent still an item,” a source close to the pair told the newspaper. “They are both focusing on work at the moment but will be back in each other’s company again soon.” Hiddleston is currently in Australia filming Thor: Ragnarok, while Swift spent the weekend in the Hamptons celebrating friend Karlie Kloss’ birthday.