Before my grandfather passed away in April 2001, he asked my mother to promise to never try & trace the family tree. Naturally, this has me fascinated, and leaves me wondering why exactly! I have copies of both his birth certificate and my mothers - nothing untoward; so maybe there is another (illegitimate) branch of family somewhere that we don't know about? He was in the navy, both Royal and Merchant, for many years so could easily have fathered other children abroad.
Assuming that this even is the big secret, how would I go about finding out?