Original: The union was transformed to a closer one by the Union of Lublin in 1569, which was shortly followed by the end of the Jagiellon dynasty that had ruled Poland for two centuries and Gediminids dynasty, that ruled Lithuania for about 400 years.
Simplified: The union was confirmed but also transformed by the Union of Lublin in 1569, which was shortly followed by the end of the Jagiellon dynasty that had ruled Poland for two centuries.