Complex sentence: The defeat of Poitiers and the capture of John the Good in 1356 deprived Jeanne of John's support and Yolande retook the regency, with Robert being knighted in December 1356 and declared of age on 8 November 1359.
Split into simpler sentences: The defeat of Poitiers and the capture of John the Good in 1356 deprived Jeanne of John's support and Yolande retook the regency. Robert was knighted in December 1356 and declared of age on 8 November 1359.