Complex sentence: Preston North End were founding members of the Football League and completed the inaugural season unbeaten to become the first league champions, in the same season winning the FA Cup without conceding a goal to become the first club to achieve the English football "Double".
Split into simpler sentences: Preston North End were founding members of the Football League and completed the inaugural season unbeaten to become the first league champions. In the same season, Preston won the FA Cup without conceding a goal, becoming the first club to achieve the English football "Double".