Before the ceremony he sits among other patriars on the pews in central nave of the Audience Hall.
After the ceremony ends, Lord Shattershield stays near the throne, discussing with Lady Alia Durinbold and Duke Ulder RavengardDuke Ulder Ravengard the advantages of uniting the Flaming Fist and the Steel Watch under single command (i.e. Gortash's). If spoken to, he says that the Steel Watch will turn Baldur's Gate into an impenetrable fortress.
If confronting Gortash, they party can Lord Rugger along with all other invited guests and their retinue slaughtered in the Audience hall.