Zrinski and Frankopan were executed by beheading on 30 April 1671 in Wiener Neustadt.  Their estates were confiscated and their families relocated — Zrinski's wife, Katarina Zrinska, was interned in the Dominican convent in Graz where she fell mentally ill and remained until her death in 1673, two of his daughters died in a monastery, and his son Ivan Antun  died in madness, after twenty years of terrible imprisonment and torture, on 11 November 1703. The oldest daughter Jelena, already married in northeastern Upper Hungary, survived and continued the resistance. Some 2,000 other nobles were arrested as part of a mass crackdown.  Two more leading conspirators — Ferenc Nádasdy, Chief Justice of Hungary, and Styrian governor, Count Hans Erasmus von Tattenbach — were executed . In the view of Emperor Leopold, the Croats and Hungarians had forfeited their right to self-administration through their role in the attempted rebellion. Leopold suspended the constitution - already, the Zrinski trial had been conducted by an Austrian, not a Hungarian court - and ruled Hungary like a conquered province.
Question: How many of Zrinski's children died mentally ill?
Answer: 1