Contrary to popular belief, it wasn't Professor Snape; the mysterious Half-Blood Prince of Harry Potter is said to be someone else.
Harry Potter and the Half-Blood Prince stands out as the most beloved installment, setting the stage for Harry's quest for Voldemort's elusive Horcruxes and a myriad of other changes. However, much of the mystery in Harry's sixth year revolves around the identity of the Half-Blood Prince, the enigmatic figure who left behind the textbook 'Advanced Potion Making' with numerous essential annotations, showcasing an exceptionally high level of proficiency.
Subsequently, the film revealed to the audience that the identity of the Half-Blood Prince is Severus Snape. However, when compared to the book, this concealed character could actually be another beauty.

Although Snape's confession of being the Half-Blood Prince shocked Harry Potter and led him to discard the book, the knowledge within it proved invaluable to him in both his studies and his subsequent journey to oppose Voldemort. Focusing on Harry's time in Potions class, whenever he used the textbook to brew exceptional potions, Professor Slughorn would often wistfully comment that Harry resembled his mother, Lily Evans (or Lily Potter). In reality, Lily was a favorite student of Professor Slughorn due to her exceptional talent in the subject, surpassing her peers.


With Lily's name almost always mentioned whenever Harry uses the Potions textbook, coupled with Hermione's speculation that the Half-Blood Prince could be a girl, it can be deduced that the owner of this marvelous book is indeed Lily - Harry's mother. This is something Harry had never considered, but he has wondered on occasion whether the Half-Blood Prince might be his father, James.

While there's no concrete confirmation that Lily is the Half-Blood Prince, the book serves as a crucial 'evidence' of the friendship between Lily and Snape. They were once very close friends, sharing a passion and talent for Potions. This is evidenced by the fact that Gryffindor and Slytherin students shared this class, making it understandable why Snape and Lily bonded over it. Therefore, it's likely that the majority of the notes in that book belong to Lily, while Snape is the Half-Blood Prince in name only for both of them.

On the other hand, this doesn't mean Snape wasn't skilled. He was still the most talented wizard, the owner of many unique and dangerous spells (such as the Never-Ending Sever), including counter-curses for them. However, Snape and Lily's friendship quickly ended after their fifth year due to Snape's leaning towards Dark Magic. Due to conflicting beliefs, Lily forced Snape to choose between her and Dark Magic, and the result was clear.

So overall, this book holds many layers of meaning. It can be seen as Lily's 'memento' left for Harry, the treasure of the little student that Slughorn adored, and as evidence of the pure and innocent friendship between Snape and Lily - the only thing pure and innocent in his life.
Source: Screen Rant