The spell that killed Bellatrix Lestrange in the Harry Potter series was not explicitly mentioned in the books or movies. However, based on the events surrounding her death, we can make some educated guesses.
In the Battle of Hogwarts, Molly Weasley engages in a fierce duel with Bellatrix. Molly, being a skilled witch and a determined mother, was determined to protect her loved ones and defeat the Dark witch.
One possible spell that Molly used is Petrificus Totalus, also known as the body-binding spell. This spell temporarily immobilizes the target, causing them to freeze in place. We see Molly casting this spell earlier in the series, so it’s reasonable to assume she could have used it against Bellatrix.
With Bellatrix frozen in place, Molly would have had an advantage. She then likely followed up with a more powerful and destructive spell to finish Bellatrix off. One possibility is the Reducto spell, which causes objects to explode upon impact. Another possibility is the Diffindo spell, a severing charm that can cut through objects.
It’s important to note that while these spells are mentioned in the books and movies, we can’t say for certain which one specifically killed Bellatrix. J.K. Rowling has not provided explicit details about the spell used, leaving it up to readers and viewers to interpret the scene.
To further support this speculation, it’s worth considering the context of the duel. Molly was fighting to protect her family, and the love and determination she felt in that moment could have fueled her magic, making her spells exceptionally powerful. This could explain why Bellatrix was ultimately defeated by Molly’s attack.
While the exact spell that killed Bellatrix Lestrange is not explicitly stated, it is likely that Molly Weasley used the Petrificus Totalus spell to immobilize Bellatrix before following up with a powerful and destructive spell such as Reducto or Diffindo. The intense love and determination Molly felt to protect her family may have amplified the strength of her magic, leading to Bellatrix’s demise.