It may feel like déjà vu, but really, J.K. Rowling had it all planned out from the start. Here are our favourite moments from the Harry Potter books that made us slap our heads and go, ‘Ohhh…’

When Harry walked straight past a Horcrux

It’s quite a famous moment of frustration, but one that bears repeating – with Harry Potter and the Deathly Hallows so heavily focused on Harry hunting for Horcruxes, we, as readers, couldn’t quite believe it when we realised Harry had been so close to one in Harry Potter and the Half-Blood Prince without realising.

Yes, that pesky Ravenclaw Diadem – cooped up in the very same version of the Room of Requirement that Harry had hidden his Advanced Potion-Making book in the previous year – seemed like just a dusty old tiara when Harry marched past it in his sixth year. When Harry returned to Hogwarts and the Room of Requirement during the final battle, he couldn’t believe he’d been so close – yet so far.

The fact that Harry had even hidden his Potions book so nearby was even more of a kicker.

His breath was loud in his ears, and then his very soul seemed to shiver: there it was, right ahead, the blistered old cupboard in which he had hidden his old Potions book, and on top of it, the pock-marked stone warlock wearing a dusty, old wig and what looked like an ancient, discoloured tiara.

Harry Potter and the Deathly Hallows

When Dumbledore’s ‘room full of chamber pots’ was something slightly more…

Speaking of the Room of Requirement, it also cropped up in an earlier book. We thought we were introduced to the ever-changing room in Harry Potter and the Order of the Phoenix, but actually, Dumbledore had described a room where he ‘required’ something (in this case, needing the loo) far earlier – in the previous book, in fact.

Well, Hogwarts may be huge and full of mysteries, but if something’s important it’s bound to crop up again – like our next call-back…

When the Vanishing Cabinet turned out to be pretty important

In a world full of magical objects, many of which we can only dream of having in our Muggle living rooms, the Vanishing Cabinet sounded like a great idea – until Draco Malfoy gave it a far more sinister purpose. The Vanishing Cabinet, a piece of furniture that can act as a transportation device if you have another one stationed somewhere else, was actually first mentioned in Harry Potter and the Chamber of Secrets, when Peeves was heard breaking it.

And for about three years, that was that – until the cabinet was brought up again in Order of the Phoenix, after Fred and George shoved a Slytherin student called Montague in there – not knowing where he went. When Montague finally got out, he revealed to Draco that he was caught in a limbo-place between Hogwarts and Borgin and Burkes in Knockturn Alley. It was then that Draco realised he could fix the cabinet and use it to smuggle Death Eaters into the school during his plot to kill Dumbledore.

So, in a slightly horrible way, one of Fred and George’s pranks inadvertently led to Draco learning about the cabinet’s powers, and his plot succeeding…

And to think it was just an innocent quirk of Hogwarts, once upon a time.

‘The other’s in Borgin and Burkes,’ said Malfoy, ‘and they make a kind of passage between them. Montague told me that when he was stuck in the Hogwarts one, he was trapped in limbo but sometimes he could hear what was going on at school, and sometimes what was going on in the shop, as if the Cabinet was travelling between them, but he couldn’t make anyone hear him ... in the end he managed to Apparate out, even though he’d never passed his test.’

Harry Potter and the Half-Blood Prince

When Sirius’s mirror led to an unexpected communication

Perhaps one of the saddest moments of the Harry Potter books was when Harry realised that the late-Sirius had left him a communication device – a two-way mirror where they could talk to each other when separated. Alas, Harry found the mirror far too late – Sirius had died when he finally found it.

However, in Deathly Hallows, the mirror united Harry with someone else, someone completely unexpected. Upon seeing a blue eye through a broken shard of the glass (Harry had smashed it in frustration) he thought he was seeing another long-gone friend – Albus Dumbledore. Well, he wasn’t that far off. It was actually Albus’ brother Aberforth, who ended up in possession of the mirror, using it to look out for Harry during the seventh book. And thank Merlin he did – with Aberforth keeping an eye out, he was able to send Dobby to rescue Harry and co. from a terrible fate at Malfoy Manor.

So although the mirror was such a source of sadness for Harry, it also saved his, and his friends's, lives two books later.

Fun extra fact about this one – you could argue that Aberforth having the mirror was foreshadowed earlier on in the book when Harry mistook a book with Albus Dumbledore’s face on it for the late-Hogwarts headmaster looking out from a mirror

Angrier than ever, he proceeded to grope in the bottoms of the vases and baskets of dried flowers, but was not at all surprised that the locket was not there. He gave the office one last sweeping look, and his heart skipped a beat. Dumbledore was staring at him from a small, rectangular mirror, propped up on a bookcase beside the desk.

Harry Potter and the Deathly Hallows

Although Harry was mistaken, it’s interesting that another Dumbledore was looking out at him through a mirror. Coincidence?

Dumbledore’s will

Deathly Hallows was nostalgic in many ways. Just look at the start of the book, where Harry is packing his bag and comes across old items from past Hogwarts adventures – such as POTTER STINKS badges and his old Sneakoscope. Ah, good times.

And then Dumbledore’s will comes along, which gifts Harry a Snitch from one of his first Quidditch matches, and Ron a Deluminator – a device which puts out lights. Both items were first seen in Harry Potter and the Philosopher’s Stone, and both end up being hugely significant in their final adventure. While the Deluminator encourages Ron to return to the Horcrux hunt after leaving Harry and Hermione, Harry’s Snitch opens right at the very end of the Battle of Hogwarts to contain one of the Deathly Hallows – the Resurrection Stone. Without the Stone to temporarily bring back the echoes of his parents, Remus Lupin and Sirius Black, would Harry have had the strength to face Voldemort? Who knows.

What are some of your favourite Harry Potter call-backs that you've spotted while reading the books?