Culprit 1

As I noticed his eyes towards me I could tell that there's something fishy. Since I already knew that there was poison in my wine I took a cup as the maid poured wine in my cup. I went up to the fourth prince and gave a toast to him. As he stood up I exchanged the cups with him. He started staring at the cup while I drank my part. Then I asked him to drink and since he resisted all the attention came towards us. Now the second prince also insisted him to drink. Finally the prince threw away the cup saying the wine is poisoned and the second prince as well others were surprised. Then I asked him why he would say so after all I was the one who brought the wine to you. Now he didn't have an answer. To this I added - unless you knew that it was poisioned by someone or maybe you yourself...