Which episode did Daenerys Targaryen lose her dragon, Viserion, to a White Walker's spear?
The Night King, the leader of the White Walkers, threw a spear at Viserion, which killed him.
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.
### Instruction: Which episode did Daenerys Targaryen lose her dragon, Viserion, to a White Walker's spear?
### Input: 
### Response: The Night King, the leader of the White Walkers, threw a spear at Viserion, which killed him.