Hogwarts is back in session, sparking a fresh wave of ‘Pottermania’.

The first teaser for HBO’s new Harry Potter series has sent shockwaves through the franchise’s global fandom, with millions of viewer reactions flooding social media in the wake of its surprise release.

The almost two-minute clip — posted without warning on Thursday — offered a brief glimpse of some of the famous moments from the start of the first book, and a little bit more.

Snippets of vision include the letter from Hogwarts addressed to the “cupboard under the stairs”, along with scenes inside the Dursley home, the Hogwarts Express and of course the famous magical school.

Loveable Rubeus Hagrid, played by Nicholas Frost, is seen making a snow angel and speaking with Harry Potter, now played by young Dominic McLaughlin.

Young newcomers Arabella Stanton and Alastair Stout play Hermoine Granger and Ron Weasley, while acting legend John Lithgow plays Albus Dumbledore and also makes a quick appearance in the trailer.

Within an a few hours, the teaser had racked up more than three million views on YouTube alone.

TikTok was soon flooded with theories about the show’s tone, timeline and cast, while X quickly split into two camps: fans celebrating the return of the wizarding world, and others questioning whether the franchise should be rebooted at all.

“Looks promising but the movies still own our childhood magic,” one person posted on X.

“The magic is back, I feel like I’m 10 years old again,” another person said.

Another person wrote: “This trailer is technically impressive — strong production values and a darker, more book-faithful tone — but let’s be honest: it’s a completely unnecessary remake that risks diluting the irreplaceable magic of the original films.”

However, some fans questioned some of the casting choices, including Stanton as Hermoine and English actor Paapa Essiedu as Severus Snape.

“How are they going to race-swap some of the most important characters in the story?” one person commented.

“This show is over before it even begins.”

However, many people noted the Harry Potter books only mention Hermoine’s brown eyes and frizzy hair — with author J.K. Rowling saying “white skin was never specified” for the character — and the adult character has been portrayed by several black actors in The Cursed Child stage productions, including by Noma Dumezweni in the original West End season.

Meanwhile, others pointed out descriptions of Snape in the books simply mention a “sallow” complexion — which can apply to any skin colouring.

Despite any controversy, by day’s end one thing was clear: HBO didn’t just release a teaser — it re-opened a cultural portal millions of fans were not ready to close.

The full trailer is expected later this year, with the series due out around Christmas.