At the end of Episode 8, a servant for Alicent leaves the castle and heads into Flea Bottom, where she sees Mystaria, a brothel employee and Daemon's former lover. This is the same servant who had a tea on hand for Alicent to give a young maid who is raped by Aegon.
Right after we see the servant meet with Mystaria, we cut to a scene of Viserys and Alicent in bed. Alicent gives Viserys a liquid to drink which may be milk of the poppy.
Not long after, it looks like Viserys dies. Does this mean the servant poisoned the king on House of the Dragon? To be fair, he's already pretty close to death at this point. But if Alicent gives him a lethal dose of milk of the poppy, whether she means to or not, in those final moments of the episode, it could be what does him in for good.
Watch House of the Dragon on Sundays at 9 p.m. EST on HBO and HBO Max.