I wasn't paying close attention when one of my Portuguese explorers passed away. I mistakenly grabbed the wrong fleet - which was led by a similarly named but still living explorer - and combined it with another explorer's fleet. When I realized my mistake I tried to separate the two explorers. No way. Usually the 'Split' button will split a fleet into two fleets and give each a leader if there is more than one already there. In this case the 'Split' button is greyed out. Any thoughts on how I get out of my predicament? 