 Complete the following phrase:  His wife Hedwigs mother Barbara Zápolya was a sister of John Zápolya, who had claimed the vacant throne of Hungary after King Louis II was killed in battle against the Ottoman Empire in 1526. However, Joachim supported Ferdid of Habsburg, who also claimed the crown and challenged the Turkish invaders. In 1542 Joachim assisted Ferdid against the Ottomans at the 