According to Esuteru (via Siliconera), it will release on October 26. However a Tweet from the official PlayStation account (which has now been deleted) lists the date as October 25. This could simply be a case of different dates in different regions or on different platforms, so IGN will update you when we know more.
The Tweet also listed the DLC’s title as Ashes of Ariandel, and suggests a trailer will soon be on the way, although the link remains private for now. Esuteru’s report says the DLC will feature new weapons, new magic, and a player-versus-player exclusive map called Immortal Competition.
The report includes images of a colorless flaming sword, as well as an ice storm spell and “one that looks like a circular boomerang made of light.”
In Japan it will cost 1,200 yen (around $12), while a season pass containing both the first and second DLC will cost 2,000 yen (around $20).