WARNING: The Following Article Contains SPOILERS For Domino #3.

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Domino - the sassy mutant mercenary who is more popular than ever thanks to a major role in Deadpool 2 - is as famous for the distinctive mark that encircles her left eye as she is for the mutation that makes her super lucky. Yet the nature of this mark has never been revealed... until now!

Created by writer Fabian Nicieza and artist Rob Liefeld in 1992, Domino first appeared in X-Force #8. Born Neena Thurman, Domino was one of many young mutants who was discovered at a young age and experimented upon by a secret government project intended to create the perfect warrior. Domino was the only test subject in her group to survive the process, though her luck-based powers were considered unreliable and unsuitable for their intended purpose. She managed to escape before the scientists experimenting on her could end her life, however, and went on to join the mutant mercenary team X-Force.

Related: Domino Gets A Comic Series Just in Time For Cinematic Debut in Deadpool 2

Most readers presumed that Domino's unique black-and-white coloration and the distinctive mark around her eye were a side-effect of her mutation. Certainly many mutants in the Marvel Comics world  acquired unique physical alterations or had their skin change color when when their powers first manifested. However, a flashback in Domino #3 - the latest issue of Neena's solo comic book series - reveals the dark truth behind her mark.

Domino And The Origin Of Her Birthmark

The flashback reveals that a ten-year-old Neena was given a kitten during her time in captivity. Originally presented as a birthday present, it was really meant to give her captors additional leverage over her, helping them to force a trauma that would make her mutant power manifest more readily. As one scientist, Dr. Rossini, threatened the kitten with a taser, the scientist holding the kitten (who it turned out was allergic to cats) suffered a sneezing fit that knocked him off-balance and into Dr. Rossini, who accidentally shocked him with the taser.

As Dr. Rossini called for a medic for his colleague, he also instructed the guards to take Neena and brand her, like all the other test-subjects whose mutant powers had been confirmed. When asked if they should place the brand between her shoulder blades like the other subjects, Rossini replied that he wanted Neena's face to be branded so that she would remember what she did every time she looked in a mirror from that day forward!

The idea that Domino's famous "birthmark" is actually a brand meant to torment her is a shocking conceit. Such twisted fare is common for writer Gail Simone, who first found mainstream fame as a writer on Deadpool. It's impossible to say what Simone may do with Neena in future issues of the Domino solo series' but it's sure to be interesting even if it is not quite so revolutionary as this issue's dark retcon.

More: 16 Worst Things Domino Has Ever Done

Domino #3 is now available from Marvel Comics.