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.