Those of you who are familiar with the books and films, which, let's face it, is everyone, will know that the pair don't quite see eye to eye for the majority of their time together.
Now - sorry for the spoiler - but by the end of the series it becomes clear that all is not quite as it seems, with Snape giving up his life for the young wizard.
We also learn that Snape was deeply in love with Harry's mum, Lily, when they were both students at Hogwarts and was heartbroken by her death.
Fans of the books, however, spotted something in the first words ever uttered by Snape to Harry, which they believe hinted at this shocking revelation.
In The Philosopher's Stone, both in the book and the film, Snape asks Harry: "Tell me, what would I get if I added powdered root of asphodel to an infusion of wormwood?"
According to Potterheads out there, the real meaning behind his words were down to the following: "According to Victorian Flower Language, asphodel is a type of lily meaning, 'My regrets follow you to the grave' and wormwood means 'absence' and also typically symbolised bitter sorrow.
"If you combined that, it meant, 'I bitterly regret Lily's death'."
But while most of us assumed that Snape hated Harry and was trying to do away with him at every turn, the actor who played him in the films, Alan Rickman, knew all along what lay in store for the characters.
In the upcoming Harry Potter 20th Anniversary: Return to Hogwarts, Rickman's former co-stars speak about how much they had known about the future narrative while filming, with Sirius Black actor Gary Oldman saying he wishes he’d had the ‘whole picture’.
Daniel Radcliffe, who played the titular wizard in the films, also admits he didn’t know everything either.
"Just Rickman,” Radcliffe tells Oldman in the forthcoming reunion special.
"He had the inside line. He very, very early said to Jo, he was like, ‘I think I need to know what happens’.”
Oldman laughs: “Rickman would have an in, wouldn’t he?!”
Radcliffe continues: “And he never told Chris [Columbus], he never told anyone. Chris would literally say to him, why are you doing that like that? He was like I’ll tell you later..."
In a 2011 interview with the LA Times' Hero Complex, Rickman said he had always known his character was going to be a 'double agent'.
He said: “Rumour has it that she put the ending in a bank vault when she was writing the beginning.
So she held it all in her head, all seven books. It’s jaw-dropping, really.
"When we started she had only written three of the books so it was like trying to walk down two potential roads not at all knowing what the end would be but having some sense of what that man’s life was.
"I knew with Snape I was working as a double agent, as it turns out, and a very good one at that."
Featured Image Credit: Warner Bros.
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