It usually goes into the state slush fund like tax revenue, AKA the crown.

In this case, it's claimed that it was 'donated to charity'.

In this case, it was being spent on upkeep/repairs/renovations on properties that are rented out, with the rent going to the 'privy purse' - the king's personal funds, not the state's funds. Spending the money to improve the properties directly increases the rent that can be charged, and offsets upkeep costs that would otherwise come out of the rent.

Money laundering.