It was the fate of King Alexander and Queen Draga in the June 1903 coup in Serbia, though they'd been killed beforehand. The event's importance extended far wider as the new regime was considered pro-Russian, its predecessor closer to Austria-Hungary. Hence it was a fairly hot topic, beyond gossip about the royal couple: it can indeed be seen as a key stepping-stone to the First World War (and leading conspirators were later associated with the irredentist Black Hand). The 1904 peak just reflects publication lags.