It is a deep green coat dress by Emilia Wickstead. The top of the coat is fitted to the waist that flares into a full skirt.
This is a beautiful coat, the colour is very nice and Kate wears it perfectly.
1) The Duchess of Cambridge wore the coat dress on 17th March 2012 for the St Patrick’s Day military parade at Mons Barracks in Aldershot, Hampshire. She wore it with a black leather belt.
2 – Kate wore it again for the same event the following year on 17th March 2013. This time she wore it without the belt as she was five months pregnant with Prince George.