Can't say I'm a fan, given the potential effects on the flight-deck environment and staff morale.
If you knew the guy you would realise how wrong you are. Do not for one moment compare the Dutch Royal family with the British one.
I am astounded at the some of the cynicism and BS on this subject. King or not, I for one am confident that he wouldn't be let loose as an F/O on passenger flights if he didn't meet the required standards. Perhaps we shouldn't let rock stars captain B757s either!