Complex sentence: Gardner and his first wife had separated in the early 1930s, and after her death in 1968 Gardner married Agnes Jean Bethell (1902--2002), his secretary since 1930.
Split into simpler sentences: Gardner and his first wife separated in the early 1930s. In 1968, after her death, Gardner married Agnes Jean Bethell (1902--2002), his secretary since 1930.