If I were him, I'd ask River to do the explaining. Maybe River can also bring Brian to where the Ponds are, since she's not bound by the same rules that prevent the TARDIS from visiting the ponds (that one, I don't get. I get that the doctor can't visit the time they were stuck in as it could lead to yadda yadda time explodey thing, but what makes River and her timetravel wrist thingie different?)