The reveal was unintentionally leaked by metadata on the European PlayStation Blog, in which various images on a new PlayStation VR Worlds post are labelled "PS Now on PC Announce Post".
The announcement post doesn't yet exist, but you should probably expect to see it very soon.
It hasn't been a great day for Sony. Earlier today it was revealed that the PS4 Slim would ship with a new DualShock 4 controller, even though the console has still to be officially announced.
Then, Sony leaked the release date for Dark Souls 3's first DLC expansion ahead of an official announcement from publisher Bandai Namco. A wireless adapter for the DualShock 4 has also shown up on Amazon France, again ahead of any official announcement.