Seeing as the convo has come back round to this i thought I'd comment.
The thing about mary is that her great grandson charles II had a ridiculous number of bastard children that we know about and probably plenty more we don't know about. If you have any connection to the british aristocracy however distant you almost certainly have one to charles and therefore mary. By extension also both the kings of England and the kings of Scotland.
It is a massive social faux pas to attempt to claim such distant ancestry in the UK. American tourists in particular are caricatured as claiming to be descended from robert the bruce as proof of scottishness. Bearing in mind that the British isles' population has been very insular for about a thousand years; to the point that almost everyone is related to the Somerled's, the Macalpines, the O'Neils, the plantagenets or the cadets thereove. In the UK and most of Europe someone is generally only considered 'descended' from someone if it is a direct male line descent. It is considered pretentious as all hell to claim descent from a line that is functionally extinct like the stewart monarchs or the carpets or karlings- despite the fact that a ridiculous %of europeans are distant relations of Charlemagne
If tumblr didn't have such racist attitudes towards white people and complete willfull ignorance of white cultures outside the usa i've no doubt we'd be seeing tonnes of snowflakes claiming to be european royalty. thankfully we are spared legions of genderspecial princesses.
I am a little surprised there isn't more scottish appropriation on tumblr- i would have thought a culture where men have the option to wear underwear optional skirts would be right up tumblrs alley.
Edit by happy coincidence the guardian just published this:
http://www.theguardian.com/science/...-genetic-ancestry-charlemagne-adam-rutherford