It depends on what sort of relationship you have with your boss, but I think it would be worthwhile explaining to him exactly what you have put above, as an Employer I would much rather have an open and honest relationship with my employees and would certainly value their honesty in return.
It begs the question however where this lady got your details from and why they are pursuing you, perhaps your boss has already spoken to his "friend" and feels you would be more valued and have better career progression somewhere else.
Theres no harm in having a general chat with your boss, especially as your hours are about to change, and mention about the firms career progression - see what he says!!