The author of the book, The DaVinci Code admitted that he got his ideas from a book about the bloodline of Jesus in relation to the "holy grail."
 
I have the book, "Bloodline of the Holy Grail, The Hidden Lineage of Jesus Revealed," by Laurence Gardner.  It is not the exact same book the author mentioned, but it is the same research vein.
 
In my book, they have the list of genealogy right from Adam to Jesus, probably taken from the Bible.
 
And they are very detailed about various "royal lines" from fairly modern days back to Joseph of Arimathea (James the Just), whose tomb Jesus was buried in, and who is purported to be the (by blood) uncle of Jesus.
 
But that is where the research falls short.  The so-called blood linkage to Jesus does not have substantial proof, IMHO.
 
Anyone who has done genealogical research, and I have, will know that "my uncle's genealogy is not  actually mine" !!! as far as Direct Line (blood line) goes.
 
Praise God for the PURE, UNTAINTED BLOOD OF JESUS CHRIST, by which we believers are saved by faith, and faith alone, not works.  The bloodline of Jesus stops at the cross.
Praise His Holy and Perfect Name.
 
By the way, in my book, on page 438, Alfonso XIII, is listed .  He is the grandfather of Juan Carlos, King of Spain.  Juan Carlos' wife, also has "royal lineage."
 
IHS, Gloria McCrea