In
1375, John suffered from a
head abscess that caused frequent fevers. He eventually recovered in September of that year. In
1384, John participated in his cousin 's war against
Peter IV of Aragon. That same year, John was reportedly poisoned. Popular belief at the time held that his brother-in-law, , was responsible, poisoning him during a feast hosted by the cardinal
Hugues de Saint-Martial. The poison was said to have caused all of John's hair and nails to fall off. Though he was eventually cured, the incident left him mentally troubled for the rest of his life. On 22 March
1386, John's father,
John I, wrote his testament, naming John, his only male heir. Two days later, his father died, and John succeeded him as Count of
Auvergne and
Boulogne. John's reputation as an administrator was poor, as he granted much of his land to his son-in-law,
John, Duke of Berry. While historian
Étienne Baluze suggests that John died shortly after writing his testament, other sources assert that he died on 28 September
1404, having entrusted his domains to his daughter. == Family and issue ==