The Tyrael’s Charger mount was recently made available for purchase in the in-game and Battle.net shop for $25. This is a limited-time offer, with only one more week remaining.
Tyrael’s Charger on Battle.Net Shop
The item Tyrael’s Charger was announced as part of Blizzard’s Holiday Sale. A postscript on the announcement mentions that the offer is only available through January 2, 2023.