Juan Carlos made his own life, I do not think he asked anyone for permission or explained what he did or did not do. If he had had to explain what he was doing, many would have stopped him.
What's more, Juan Carlos has a certain reputation for being miser (and especially with his son, it seems that he has helped his daughters more), and from what we discover, he was much more splendid with his friends than with his family. He is also quite old-fashioned, so he left the bargain to Felipe to help the women of the family, instead of giving each one a part.
Let's say he followed a "family tradition", his father and grandfather had an account with similar characteristics to help the family. In these foundations, the beneficiaries only have powers upon the death of the owner, and it is possible that not only did Felipe appear, but in case something happened to him, he would have appointed other substitutes.
In any case, the foundation closed in 2012 and all the money ended up in a Corinna account ... I don't think he asked her son for permission either.