Merchant of Venice Act 2 Scene 9 Who is the noble prince reffered to in the first line ? What is the context of Portia's speech ?

The Prince of Aragon arrives in Belmont and decides to choose from among the three caskets. Portia takes him into the room and makes him recite the oath never to reveal which casket he chooses, and further to promise never to marry should he choose the incorrect casket. The Prince of Aragon agrees and starts to read the inscriptions.