"Players who level a World of Warcraft character to level 20 will earn a new Achievement, Fledgling Hero of Warcraft, that will unlock Liadrin for use in Hearthstone. No World of Warcraft subscription is necessary to earn this hero and bring the power of the Light to bear in Hearthstone—simply log in to your existing World of Warcraft account and play.

Note that while the World of Warcraft Achievement will not be rewarded retroactively, anyone who leveled a character to level 20 after 11 a.m. PST on March 11 will be eligible to receive Lady Liadrin.

The first three heroes in Hearthstone cost $10 so it's nice to see one that you can unlock for free. World of Warcraft subscription or not you can unlock this hero using your normal account or WoW starter edition which is free to anyone with a Battle.net account.