No, unfortunately they are a former gunslinger that was the Calamity's best friend and were killed a while back. :(
There are a couple homebrew playbooks, the Legacy and the Huckleberry, that would work as Blackheart. The Legacy can be found on the Gauntlet's Discord server and the Huckleberry is here: https://mcawesomerson.itch.io/the-huckleberry