Complex sentence: The date of Catherine's birth is not known; the earliest source that mentions Catherine is the will of her maternal great-grandmother Jelena Lazarević, who left her some jewelry, dated 25 November 1442.
Split into simpler sentences: The date of Catherine's birth is not known. The earliest source that mentions Catherine is the will of her maternal great-grandmother Jelena Lazarević, who left her some jewelry, dated 25 November 1442.