Haymitch calls Katniss "sweetheart" from the very beginning, but Sunrise on the Reaping explains she's not the first he's bestowed it upon.

Your heart was probably prepared to be broken by Suzanne Collins’ new novel Sunrise on the Reaping, the tragic story of how Haymitch Abernathy won the Hunger Games and lost everyone he loved. But were you ready to learn so much about Katniss Everdeen’s family as well,

Haymitch Abernathy’s time in the Hunger Games is at the center of Suzanne Collins’ newest prequel book, Sunrise on the Reaping. Set 24 years before the events of the first novel featuring Katniss Everdeen (played by Jennifer Lawrence in the film franchise) and Peeta Mellark (Josh Hutcherson),