Do we know if Delphi's claims are true?

Question

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.

Answer 1

They probably are

Consider:

• She can

  speak Parseltongue.

  This is mentioned in the question, but it bears examination, since this is a rather strong piece of evidence. Recall that Lord Voldemort was the last known speaker of Parseltongue:

  “You can speak Parseltongue, Harry,” said Dumbledore calmly, “because Lord Voldemort — who is the last remaining descendant of Salazar Slytherin — can speak Parseltongue.”

  —Harry Potter and the Chamber of Secrets

  All known Parselmouths, beside Herpo the Foul, descended from Salazar Slytherin. And who is to say that Herpo may not have been Slytherin's ancestor. Given the rather small number of magical families in Britain, and Dumbledore's extensive research into Voldemort's past, I think we can trust Dumbledore to know both the nature of Parseltongue, and who is descended from Slytherin.

  Who would

  her parents

  be otherwise? Rodolphus? Euphemia Rowle? I think Dumbledore would have known if Rodolphus or the Rowles were descended from Slytherin.

  This is a strong piece of evidence.

• The prophecy:

  DELPHINI: Voldemort will return and the Augurey will sit at his side. Just as it was prophesized. “When spares are spared, when time is turned, when unseen children murder their fathers: Then will the Dark Lord return.”
  
  —Harry Potter and the Cursed Child

  This fits rather well with the events of the play. Time was turned, certainly.

  The Dark Lord returned, both in the bad future, in the past, and in the metaphorical sense.

  Spares were spared, clearly, in the case of Cedric Diggory.

  It seems reasonable to suppose that the rest of the prophecy was fulfilled, then: unseen children killing their parents. Admittedly, both:

  Harry and Albus

  count, but I think Delphini is another strong possibility.

Is this definitive proof? No. All this evidence, combined with Delphini's own claims, merely makes her assertions seem very probable to me.