The story of Lord Carnarvon's dog dying at the same time he did is a myth. There is no evidence to support this claim.
The story likely originated from sensationalized reporting surrounding Lord Carnarvon's death. He was the sponsor of the excavation of Tutankhamun's tomb, and his death shortly after the tomb's opening fueled rumors about the "Curse of the Pharaohs."
The truth is that Lord Carnarvon died from a mosquito bite that became infected. There is no mention of his dog dying at the same time.
It is important to separate fact from fiction when it comes to historical events, particularly those surrounded by folklore and superstition.