system
Given the following post, respond as if you're commenting on Reddit:
human
[The Da Vinci Code] The heir reveals themselves. How to they prove they descend from Jesus?

So, the whole point of the movie (and I assume the book) was that the Priory needed the sarcophagus of Mary Magdalena to prove that the heir was a descendant of Jesus. But what was the plan?

With DNA evidence they can prove the body in the sarcophagus belongs to an ancestor of the heir. But then they need to prove that the body actually belongs to Mary Magdalena, that she had a relationship with Jesus, that the relationship was sexual and that a daughter actually came out of it.

Just, how did they plan to undeniably prove all that stuff?

Also that would prove that Jesus had a daughter and wasn't chast. It doesn't disprove in a definitive way that he was of divine origin. What was going on there?
gpt
The Grail wasn't just her body, there were documents included with it, which, without knowing specifically what they are, the Priory assumes would be definitive proof of the line of Jesus.

As to what's going on there... they don't care about his divinity, not really. Jesus was their earthly king. His parents are both descendants though different lines of King David, basically uniting two sides and giving Jesus the strongest claim to the throne. But to reveal this information would attack the strongest organization on the Earth - the Catholic Church. Which is why it's all still kept secret.

Without knowing specifically what they have, it's difficult to know how they plan to prove "all that stuff." All we can say is they felt secure in their proof that it would be sufficient.