Actually, the solution is very simple. The bf and gf meet the
ex-bfs together. This will avoid misunderstandings, white lies,
ex-bfs developing rekindling passion, etc...
Since it's just normal friends, I don't see the problem with this
approach. Also, being open about friends build trust in a
relationship. Indirectly, it also signal to the ex-bfs that the gf
and bf is happy together.