Were they daughters of a sovereign? Did Princess Marie inject some significant royal blood in the Princely lineage? Thanks.
They were the daughters of Prince Louis of Lorraine, Count of Armagnac, a cadet branch of the House of Lorraine and part of the French House of Guise. They were members of the 'Household' of the King of France.
Isn't Mary Queen of Scots from the French House of Guise through her mother? That would somehow then link the Grimaldis with the royal "big leaguers" :-)
True, but that is not the only connection. For example, Prince Louis II's mother was the daughter of the Duke of Hamilton and so Prince Louis II, Prince Rainier III and Prince Albert II are all, by that line, descended from the Stuart kings of Scotland (and James I of England).