Warning – contains SPOILERS for Stranger Things season 4, volume 1.

The identity of Eleven’s (Millie Bobby Brown) father may always be up for speculation, but one mind-blowing Stranger Things theory suggests a potential answer. After escaping Hawkins National Laboratory in 1983, Eleven always struggled to find a truly stable family situation. Her time with Jim Hopper (David Harbour) seemed like a difficult, albeit permanent situation until his perceived death in Season 3. At that point, the Byers brought Eleven into their family and relocated to California. Stranger Things season 4 shook Eleven’s familial situation slightly more when Joyce (Winona Ryder) left with Murray (Brett Gelman) to rescue Hopper at Kamchatka, therefore becoming removed from Eleven’s life for an indeterminate period of time. Not long after Joyce and Murray left for Russia, Eleven returned back to the clutches of Dr. Sam Owens (Paul Reiser) and surprisingly, Dr. Martin Brenner.

Potential candidates for Eleven’s father like Dr. Brenner (Matthew Modine) carry reasonable evidence, but nothing’s confirmed. Stranger Things season 2 revealed that Eleven’s biological mother was a woman named Terry Ives (Aimee Mullins), who began to take part in MKUltra in 1969. Eleven was born in 1971, meaning that Ives was pregnant with her while she was still involved with MKUltra. The Stranger Things prequel novel Suspicious Minds reveals that Eleven’s father is a man named Andrew Rich, who was dating Ives during her time with MKUltra until his death fighting in the Vietnam War. With that said, the novels sometimes contradict the show rendering their status in canon questionable at best. In the meantime, Stranger Things itself never sets up an official answer.

Related: How Max Really Escaped Vecna (It Wasn’t Just The Music)

However, one theory (via Reddit) proposes a wild yet strangely plausible answer to who Eleven’s father is. After Dr. Brenner took him in for long-term experimentation, Henry Creel became Number One (Jamie Campbell Bower) and eventually Vecna, Stranger Things’ powerful season 4 villain. The theory suggests that Dr. Brenner created his subsequent test subjects by actually using Number One’s semen, who at the time of at least Eleven’s birth would have been of age. If this theory were true, then One’s connection with Eleven is much stronger than believed and makes Stranger Things moments like the Hawkins Lab Massacre much more sinister. Here is the theory explained further in-depth.

Eleven’s Father is Number One

Dr. Brenner recognized the potential that Henry Creel/Number One had. While not all test subjects after One may have been produced with One’s DNA, it’s not too implausible to believe that Brenner would have taken advantage of Number One’s genetics in this way. Number One and Eleven formed a close bond together, with Number One confiding in her and helping her try to leave Hawkins Lab. While Stranger Things reveals One’s identity and proves that he was massively manipulating Eleven, it’s clear that Number One found a powerful connection with her. Eleven’s abilities also share similarities with One’s. A primary example of this is the fact that her telekinetic powers respond to One’s advice on finding a memory that’s considered both “sad” and “angry.”

Eleven’s brown hair and eyes may seem to offset this theory at first glance, especially considering that her mother shares the blonde hair and blue eyes that One has. However, One’s younger self is shown with darker hair. Furthermore, Eleven’s hair and eyes could have been carried down by Victor and Virginia Creel, respectively. With that said, because Stranger Things includes highly powerful characters like Eleven who would otherwise not exist in the real world, anything is possible in the secret confines of Hawkins Lab – including some genetic dissimilarities. For example, it’s possible that Dr. Brenner altered Eleven as an embryo to remove or add certain genes, whether it be to hide the fact that One is Eleven’s father or for another reason entirely. Whatever the case may be, there is a major piece of evidence proving the Stranger Things father theory: Brenner’s motive to create more subjects like One.

Dr. Brenner’s Test Subjects Got Their Powers From Number One

To assume that Dr. Brenner’s subjects gained their abilities through psychedelics and sensory deprivation salt baths alone is faulty. While those tactics could elicit and strengthen extraordinary powers, Stranger Things season 4 suggests through Henry Creel the possibility that psychic abilities could be innate. Therefore, it’s reasonable to believe that the Hawkins Lab kids in Stranger Things could have some kind of implanted genetic predisposition to the kind of powers Dr. Brenner would want to develop in them. Eleven’s mother was part of Brenner’s MKUltra experiments and would have been subject to whatever controlling, manipulative tactics he would have used on her. Hawkins Lab instates thorough and ethically-breaching procedures to assure that the parents never contact their kids. Understandably, Hawkins Lab is selecting their test subjects on something stronger than chance. Brenner isn’t testing whether the kids are psychic or not. Instead, Brenner is actually training them, as evidenced by the competitive situations he puts the subjects in, the discipline he provides, and the psychically-stimulating environments his subjects are constantly exposed to. Developing his subjects from One is devious, but it would be in line with Brenner’s character.

Related: Old Stranger Things Characters Who Return In Season 4

Number One Father Theory Makes Hawkins Lab Massacre Way Worse

Eleven banished One/Vecna into Stranger Things’ Upside Down after he massacred everyone at Hawkins Lab. This is an already horrific act that becomes compounded further with Netflix’s content warning for the scene reminding viewers of the massacre’s tragic realism. However, the Stranger Things theory about One makes the massacre even worse, for it would mean that One is killing his own children. One already displayed a harsh disdain towards humanity, which fuels his motives as Vecna and helps him kill the Hawkins Lab victims without hesitation. In addition, One’s Hawkins Lab massacre is vengeance-fueled. However, to extend such murderous hatred towards his own children makes One even crueler than perceived. Number One may not know they’re his children, which despite his psychic abilities is still possible considering how clandestine the operations are at Hawkins Lab. Even so, this obviously doesn’t excuse his heinous actions.

Why An Eleven-001 Father Reveal Is A Perfect Stranger Things’ ’80s Homage

The theory does have a lighter note. With each passing season, Stranger Things’ list of ’80s references continues to grow. While some homages are more overt, like the season 4 cameo by ’80s horror legend Robert Englund, some nostalgic nods are more hidden. The Darth Vader plot twist in The Empire Strikes Back is one of the most iconic moments in ’80s cinema, so it would be appropriate for Stranger Things to wink at that somehow. One shares similarities to Anakin Skywalker, for he too becomes a completely changed entity due to the corruption of darker forces, who went on to slaughter innocent children prior to being physically transformed. If One/Vecna is Eleven’s father, Eleven becomes the perfect Luke Skywalker stand-in, searching for her father for the ultimate showdown between good and evil. While Stranger Things may never reveal Eleven’s real father, much less confirm that her father is One, such a possibility would connect the two characters in deeper ways than originally perceived.