The Cottagers have backed the Spanish coach so far in the transfer market ahead of his debut Premier League season at Craven Cottage.
Arbeloa has already paid out £44M to his old club Real Madrid, to bring in Gonzalo Garcia and Cesar Palacios, and the deal for Charles will make the former Manchester City academy star the most expensive Northern Irish footballer of all time.
Charles scored six goals for the Saints last season, as a real driving for in their midfield, before missing out on the EFL Championship playoff final following the controversy of Spygate.
The 22-year-old will sign a five-year deal in London and he could make his Fulham debut in their final preseason outing - up against Bundesliga side VfB Stuttgart on Saturday 15 August - before a Premier League bow against local rivals Chelsea on August 24th.