The fox was feeling blue when it went into a hotel lobby at Travel Lodge in Woolwich and looked a little bit confused.
This image was tweeted by hotel guest Scott Farnell @fazzy87 and retweeted on social media.
It very soon attracted mainstream media coverage on the BBC, ITV News and London newspapers.
A spokesman for the RSPCA said that they had not received any calls about this very unusual case at their 24 hour helpline, but would ask anyone who sees the fox to call on 0300 1234 999.
The spokesman also said the RSPCA had not seen a blue fox before and had no idea how it had managed to become that colour.