In the 1990 Nepal constitution the Executive powers of the Kingdom was entirely in the hands of the King. According to the Interim constitution drafted in 2007, the executive powers of Nepal are in the hands of the council of ministers headed by the Prime Minister.
There was a dire need for a new constitution as the ideals of the people had changed as the country had moved from a monarchy to a democracy. The old constitution was drafted when the country was under the rule of the king. The people of Nepal fought for a democratic government for many years. So the old constitution does not reflect the ideals of the people. The new constitution will change the rules of the old constitution in order to bring in a new society with new ideals.