Complex sentence: Lothair's brief "reign" came to an end with his death on 22 November 950, and Berengar II was crowned king on 15 December, with his son Adalbert of Italy as co-ruler.
Split into simpler sentences: Lothair's brief "reign" came to an end with his death on 22 November 950. Three weeks later, Berengar II was crowned king with his son Adalbert of Italy as co-ruler.