Complex sentence: The couple did not discuss Pierrepoint's "other career" until after he had travelled to Gibraltar in January 1944 to conduct a double execution; although Annie had known for many years she did not ask him about it, waiting for him to raise the topic.
Split into simpler sentences: The couple did not discuss Pierrepoint's "other career" until after he had traveled to Gibraltar in January 1944 to conduct a double execution. Although Annie had known for many years she did not ask him about it, waiting for him to raise the topic.