Jack Thorne, although a critically acclaimed screenwriter, ruined what was supposed to be J.K. Rowling’s grand finale. It might seem harsh to blame only Jack Thorne for the shortcomings of “The Cursed Child,” but the fundamental flaws of the book (and play) simply aren’t mistakes Rowling would make.

“The Cursed Child” was supposed to be the highly anticipated eighth book in the Harry Potter series, a conclusion worthy of Albus Dumbledore himself. The true result, however, ended up being more like Severus Snape: When it was good, it was really good; but when it was bad, it was really bad. Since Thorne and Rowling were the two collaborators in bringing this piece to life — and since Rowling knows her own characters better than anyone else — the mistakes in characterization of both the characters and the universe itself can only be attributed to Thorne himself.

To be fair, it was fun seeing all the characters again, some nineteen years older than they were in the original seven books. Harry Potter, now 36, is bogged down by the paperwork that accompanies his position as the Ministry of Magic’s Head Auror. He’s married to Ginny Weasley, his Hogwarts sweetheart, and is trying, really trying, to raise their three children — James, Albus, and Lily — in a happy home.

But his shortcomings in doing so is where “The Cursed Child” gets bad. Thorne’s characterization of the adult Harry Potter — especially in how he raises his children — completely disregards Harry’s own childhood. Anyone who’s ever touched a “Harry Potter” book, after all, knows that its protagonist had a miserable upbringing: He was starved, locked up, and isolated by his aunt and uncle for the first 11 years of his life.

So when Jack Thorne portrays Harry as harsh, and emotionally disconnected, toward Albus — a social outcast, just like the younger Harry — it seems strange. After the two of them have a fight, in which Albus laments how difficult it is to be the “less than perfect” son of The Boy Who Lived, Harry tells him, “There were times that I wish you weren’t my son.”

Now hold up, Jack. Harry grew up feeling unwanted. He heard things like this on a daily basis. For him to instill the heartbreak he experienced as a child into his own son is to completely mangle Harry James Potter’s character.

It gets worse: When he’s not telling his own son that he wishes he weren’t the boy’s father, Harry is oddly passive — excessively so — when it comes to managing his kids. He has many lapses in judgment when it came to parenting, well beyond the allocated amount for most other wizarding parents. He also picks one too many fights with his wife, Ginny Weasley, on how to raise their kids. It’s natural for there to be conflict between husband and wife, but not to this extent.

The real Harry that we know and love from Rowling’s seven masterpieces isn’t the type of person to fluctuate between the extremes of passive and aggressive. The real Harry would never stubbornly pick fights with his wife and verbally demean his own son.

Jack Thorne’s warped characterization of Harry does him complete injustice. And when you reimagine the main character of a book so much that you defile their relationships with the other characters, you break the entire backbone of the story. So, Jack Thorne, thank you for giving us the finale that we never wanted.