You found him basking in the sunlight after his swim.

The entire previous day and night had been spent in a protracted battle, and only in the morning had the party managed to set up camp and rest. It seemed you were not the only one who had thought to go down to the nearest river to wash. Astarion stood on the shore... naked... His body was wet from the water, his hair slightly damp and disheveled, while he, with relaxed closing eyes, basked in the warm morning sun.

Your approach was quickly detected, and the vampire spawn half-turned to you with a charming smile on his face. "Hello, darling. Decided to keep me company, hmm?"