It is interesting there seems no such equivalent, where the King and the future King, have a seat in the highest advisory board to the Government as well the supreme Court of Administration. It places the future King uniquely close to the machinery of state, on a weekly base.
Even if no political influence is executed by the furure King, in the past 5 centuries the Council of State has been the ultimate top in the who-is-who pyramid. After all: Cabinets come and go, the Council of State remains. Queen Beatrix was a member for almost 6 decades (1956-2013) and as every piece of legislation is vetted by the Council, and as conflicts of citizens with the state are judged by the Coucil, it truly is a "high school for future Kings".
Not for nothing Mr Herman-Diederik Tjeenk Willink (the former vice-president of the Council whom was Willem-Alexander's "mentor") has been asked to become a godfather to Princess Amalia, 18 years ago. The former vice-president was at this special session as well, to witness his goddaughter.