According to this theory, the Queen is a leading emissary of the alien race - sometimes referred to as the reptoids or reptilians - who uses her connections and influence to help keep a secret bloodline in power. The story is confusing and bewildering to those unacquainted with it, but takes in various broader tropes, including the Illuminati, freemasonry, the 'grays', the Bush dynasty, the royal families of Europe and the Bilderberg Group.
As well as part of the conspiracy to govern all of humanity, the Queen is said to let her hair down by eating human babies at secret meetings where she and her kin can frolic unmasked. Those familiar with stories of Satanic Ritual Abuse will recognise this as a recurring motif in tales of alleged survivors. More frequently, her guise is said to slip at unguarded moments where her eyes or ears unwittingly reveal her true identity - many such moments have been captured for the eyes of the curious on YouTube.
It is unclear as to where this theory originates, but its most vocal proponent over many years has been ex-BBC presenter David Icke. He has written extensively about the proofs he believes he has found to support his assertion and an extensive belief system has sprung up in his wake - including video evidence, huge online forum discussions and a series of books, pamphlets and publicity stunts.
Is the Queen actually an alien? As few of us are experts in either royal geneaology or alien subspecies it would perhaps behoove us to wait for clarification from either the balcony at Buckingham Palace... or the skies above.
See also: conspiracy theories