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,
Bolesław the Forgotten calendar was in use so New Year's Day had not been changed to the first day of January. The text describes him as follows: However, there is no mention of any coronation of a Polish ruler in this period, which would have to be recorded in the German sources (as was the case with the coronations of Bolesław I and Mieszko II), probably because there was no royal insignia in the country, which had been returned to the Emperor by the well-known Bezprym earlier in the year 1031. This brief description of Bolesław in the "Wielkopolska Chronicle" is very similar