Complex sentence: In July 2015, it was announced as the most-distant known object, surpassing the previously most-distant known galaxy, EGS-zs8-1, which had only been determined in May 2015.
Split into simpler sentences: In July 2015, it was announced as the most distant known object. It had surpassed the previous most distant known galaxy, EGS-zs8-1 that had only been determined in May 2015.