Mieszko the Younger time in 1166 or 1167 in a document signed between Mieszko III and Casimir II the Just at the congress in Jędrzejów as one of the sons of the Duke of Greater Poland. Between 1177 and 1179, as a result of the revolt against his father, Mieszko, with his parents and siblings, were exiled from Poland. They probably returned to the country in 1181, when Mieszko III regained the rule over Greater Poland. In 1184 and thanks to the wise diplomatic affairs of his father, Mieszko the Younger was appointed by the sickly Duke Leszek Governor of the Masovian-Kuyavian principality,
Mieszko Kazimierzowic no mention of Mieszko's influence on Polish politics. Mieszko died on 28 January 1065. Year of death was noted by "Rocznik kapituły krakowskiej", while day by "Necrologium monasterii superioris Ratisbonensis". He died unmarried and childless. Mieszko Kazimierzowic Mieszko Kazimierzowic ("Kazimierzowic" means "son of Kazimierz") (16 April 1045 – 28 January 1065) was a Polish prince member of the House of Piast. According to some scholars, he was probably Duke of Kuyavia since 1058 until his death. He was the third son of Casimir I the Restorer by his wife Maria Dobroniega, daughter of Vladimir the Great, Grand Duke of Kiev.