I have two ancestors who claimed to be of Royal Descent.
My greatx5 grandmother, Helen Lascelles (c.1758-c.1841), claimed to be related to most of the gentry/lairds in Buchan through the Lascelles - even claiming to be head of the House of Noble, and the Hereditary Constable of Broadsea. Her mother was, though, an illegitimate daughter of John Gordon who was, in turn, a grandson of William Fraser, the 12th Lord Saltoun of Abernethy. Her mother's claim seems to hold some water. Helen Lascelles claimed her mother was left £10 in John Gordon's will and sure enough, £10 was left to his natural daughter in his will. He left the bulk of his estate to his nephew, Lord Saltoun. Through the branches of the Fraser family the first monarch you encounter is King James IV of Scotland - reigned 1488-1513.
My greatx7 grandfather, William Rose (1740-1807), claimed to be a descendent of the Rose family of Kilravock. He was a noted genealogist and was able to prove his connection to the Kilravocks (he wrote to the Clan Chief who agreed with William's research). William Rose was the Factor to the Earl of Fife and was apparently a bit up himself. He had a coat of arms commissioned and, when relations turned sour between him and the Earl (Rose tried to sue Fife), he was ridiculed for his desperate attempts at portraying himself as a genry gentleman with his distant connections to the Kilravocks.
So if those two ancestors' claims are correct, there is lots of blue blood in me!