This theory keeps resurfacing.

More than 20 years later, there are still many conspiracy theories surrounding Princess Diana’s death. One persistent theory is that the late princess was pregnant with her then-boyfriend Dodi Fayed’s baby. Conspiracy theorists have fixated on the idea of her pregnancy partially because of an ambiguous comment she gave to newspapers a few weeks before her death about “a big surprise.”

After the infamous car crash in Paris that killed both Princess Diana and Fayed in 1997, the Egyptian millionaire’s father, Mohamed Al-Fayed, fueled the pregnancy idea, adding that the couple was about to get engaged soon as well. Part of his theory was that the royal family and British secret services were plotting against the marriage because they disapproved of the match. But forensic scientist Professor Angela Gallop put the pregnancy rumors to rest with her investigation documented in her book When The Dogs Don’t Bark: A Forensic Scientist’s Search for the Truth. Here are other conspiracy theories that still surround Princess Diana’s death.

Princess Diana’s blood samples from the car tested negative for the pregnancy hormone hCG. Levels of this hormone appear in a blood test 11 days after contraception, and typically, these hCG levels double every 72 hours after. “In the end, the results of all the tests were negative,” Gallop wrote in her book. “Which meant it was extremely likely that Diana was not pregnant at the time of her death, and that she had not been taking contraceptive pills.”

Still, some people don’t believe the blood test results, pointing to the fact that Princess Diana was embalmed quickly—which would have made a urine pregnancy test out of the question. The timing of the embalming, however, makes sense. Doctors didn’t see a reason to delay the process since her injuries were consistent with her cause of death. It’s also not standard practice to give deceased women pregnancy tests. It seems that no matter the explanation, people still want to believe this rumor and many others surrounding the life and death of Princess Diana. Don’t miss these 18 conspiracy theories about the rest of the royal family.