10 Harry Potter Plot Twists You Never Saw Coming

10. Severus Snape Is The Self-Styled Half-Blood Prince

Considering it is the title of the fourth film in the series, a surprisingly small amount of screen time is spent on the revelation that Severus Snape (Alan Rickman) himself is the mysterious Half-Blood Prince. The potions master blurts out his truth at the film's eleventh hour, just as Harry is trying to wield one of his own spells against him.

Most of us had long since assumed that Snape was a pure-blood wizard, on account of his sorting into Slytherin house and subsequent graduation into Lord Voldemort's cabal of Death eaters, and so we discounted him - one of the most skilled alchemists around - out of hand.

On top of that, red herrings are cleverly scattered through the film, with Harry's mother revealed to be a potions prodigy and Tom Riddle having been one of new/old potions master Professor Slughorn's favourite pupils.

Perhaps some of the film series' devotees had inklings of the Prince's potions book being the product of another of Voldemort's followers or forebears - the next baddie to enter the fray and complicate things just as Harry is heading for a collision course with his old foe.

But, alas, it was slippery Snape all along.