"Have you swallowed something funny in there? Become a Mudblood without any of us noticing? Harry Potter died over twenty years ago as part of that failed coup on the school - he was one of those Dumbledore terrorists we bravely overthrew at the Battle of Hogwarts."
-- Dolores Umbridge (CC2.20)
24 February 1995
Using the Time-Turner for the second time, Albus Potter and Scorpius Malfoy prevent Cedric Diggory from winning the Second Task of the Triwizard Tournament by using an Engorgement Charm to float him out of the water.
Albus has added a special feature as well – fireworks in the sky proclaiming that “Ron loves Hermione” – in an attempt to fix one of the other issues resulting from their first use of the Time-Turner. Their plan accomplished and time running out, they return to the future (CC2.20).
However, something has gone horribly wrong. Only Scorpius returns – without Albus – and he is met by Dolores Umbridge, who identifies herself as the Headmistress of Hogwarts.
She tells Scorpius that Albus Potter doesn’t exist (Harry Potter was killed at the Battle of Hogwarts). Furthermore, she says that Scorpius is ruining the Voldemort Day celebrations by messing about in the Lake (CC2.20).
Initially 24 February 1995, during the Second Task of the Triwizard Tournament, then on "Voldemort Day" in 2020, likely in late September or early October
This event marks the start of the Scorpion King timeline, as described in the essay "Albus Potter and the lesson in Quantum Mechanics" by Nick Moline.
The shock of what Professor Umbridge says to Scorpius is huge. Harry Potter dead? Albus never born? Voldemort Day being celebrated with Dementors in attendance at Hogwarts? What kind of world will this turn out to be? (CC2.20)
From the Web
Pottermore: Harry Potter and the Cursed Child
The theatre production opened in the West End of London at the Palace Theatre on 31 July 2016, with Sam Clemmett in the role of Albus Potter and Anthony Boyle as Scorpius Malfoy: Harry Potter and the Cursed Child, Parts One and Two