In Harry Potter and the Cursed Child, Delphi says something along the lines of
Rodolphus Lestrange telling her when she was young that she wasn't really the offspring of Bellatrix and Rodolphus, but rather that she was the offspring of Bellatrix and Voldemort.
However, when I read it, it didn't seem like fact as much as it seemed like her parents fed her some made up story hoping it would inspire her to one day become some sort of
powerful wielder of Dark Magic comparable to Grindelwald, Voldemort, etc.
Is there any proof that the stories she was told are true?
Note: I am aware that Delphi is a
Parselmouth, as was Voldemort,
but other wizards and witches have also had this in common, so I'm looking for maybe something more concrete than that, i.e. JKR quotes, book quotes, etc.