A new optical illusion debate is taking the internet by storm... and this time it has nothing to do with a dress.

Mark Millar revealed on Twitter that the first edition of his new comic Chrononauts includes a baffling illusion within a time piece on the left side of its front cover.

The majority of people who view the optical illusion, which was created by artist Sean Gordon Murphy, will see a cracked watch face, however, one in 15 can see a green hourglass on a purple background.

Millar said: "Sean's a genius, as you know, but he's also a tech geek and has created something very odd and cool on the cover of this week's Chrononauts issue one. There's an optical illusion on his cover which he's going to explain online tomorrow night, something you can see in the face of the time-piece on the left hand side."

The illusion has created a lot of debate on Twitter, with Nick Frost and Scots comedian Greg Hemphill both claiming they can see a green hourglass in the image.

Millar, who says that he can see the broken clock face, tweeted that it tends to be supercreative people who can see the green hourglass.

Millar said that Murphy will explain how the optical illusion works on the Millarworld forum tomorrow.