Fans were quick off the mark with the jokes.
"Shoot 'I Am Legend – Dad Bod edition' asap," one quipped.
Another wrote "Why you starting to look like Uncle Phil tho?", in reference to Will's late on-screen uncle in Fresh Prince of Bel Air.
One man even offered to train Smith, "Will, I'm coming to train you. For free, can't have a legend looking like this."
Lots of fans praised Smith for his realness, "That's the funniest, realest (sic) thing I've ever seen. Way to change the façade of Instagram."
Another declared, "Thank you!!! Aren't we all after this pandemic?"
One follower noted, "I finally look like my idol."
Others speculated that the reason behind the award-winning actor's new figure may be for a film.
"You've earned the right to be … enjoy life! Actually … knowing you it's for a role," one fan commented.
Smith is thought to be gearing up to begin filming Emancipation. The story sees Smith portraying Whipped Peter, an enslaved person who emancipated himself from a Southern plantation and joined the Union Army.
The film made headlines recently when it pulled out of filming in Georgia, in the US, over new voting laws introduced to the state. In a statement to Deadline, Smith and director Antoine Fuqua said they felt "compelled" to act.
"We cannot in good conscience provide economic support to a government that enacts regressive voting laws that are designed to restrict voter access," the statement said.
Some feel the new law will restrict disadvantaged groups from voting in the state.
It is the first film to pull out of filming in Georgia since the voting laws came into effect – but others may follow.
The director of the new Indiana Jones film, James Mangold, has said he would not make any new films in Georgia because of the law.
