A juvenile king penguin (Aptenodytes patagonicus) was sighted at San Martín Station, Marguerite Bay, west of the Antarctic Peninsula (68°07'S, 67°08'W) on 3 February 2020. The animal was apparently healthy. It was uninjured, moving freely between the station buildings. It remained in the area until 27 March, when it was last seen. Numerous king penguin records have been reported in recent years, mostly in the South Shetland Islands. Two chicks have even been recorded hatching on these islands, but there is currently no evidence that king penguins have raised a chick to emancipation successfully. Here we present the most southerly known record of king penguins, the only one farther south than the Antarctic Circle. Coupled with observations from other parts of Antarctica, the information presented here supports previous suggestions by other authors of a southwards expansion of this species specifically in the Antarctic Peninsula region. The presence of this species at numerous Antarctic localities suggests that the known distribution of this penguin could change in the near future in response to climate change.