Advanced Potion Making
When Severus Snape was in school at Hogwarts, he obtained his Potions book, a copy of Advanced Potion Making, signing it with his own signature and self-made nickname, The Half-Blood Prince. In the margins of this book, he wrote down many spells that he made himself, along with alteration to Potion recipies for much better effect. The spells he invented, having written them down in the margins of this book, were Sectumsempra, Levicorpus, and Muffilato. When Snape graduated from Hogwarts School of Witchcraft and Wizardy, he left the book behind.

During Harry Potter's sixth year at Hogwarts, Harry discovered the book with the nickname, The Half-Blood Prince, written inside. With the book, Harry excelled at Potions, and Snape grew suspicious. Soon, Snape discovered that Harry had obtained his book after Harry used Sectumsempra on Draco Malfoy. After the incident with the attack on Draco Malfoy, Harry Potter and Ginny Weasley brought the book to the Room of Requirment.

It was unknown if Harry Potter removed the book from the Room of Requirment, for, during The Battle of Hogwarts, a Fiendfyre was casted in the Room of Requirment.

But, this is highly unlikely, for the book was possibly destroyed due to the Fiendfyre.

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