Michael Baigent and Richard Leigh, the two authors of Holy Blood, Holy Grail who happen to be suing Dan Brown for copying too much from their book, claim to have independently noticed that sangreal, one medieval spelling for "Holy Grail" should be split as sang real, "Holy Blood," referring to the "sacred bloodline" of Jesus Christ.
Alas, lads, your word manipulation was far from new. Sir Thomas Malory makes it in one (and only one) place in the Le Morte D'Arthur by defining the" Sankgreal" as "the blessed blood of our Lorde Jhesu Cryste." But Malory clearly means that in Eucharistic not genealogical sense.
And an obscure contemporary of Malory named John Harding (1378-1465) had earlier read san greal as sang real in his longer verse chronicle of Britain. But Harding meant the royal blood of the Grail knights and a chivalric order of the sanke rioall, not the descendants of Jesus.
The latter tidbit of information comes from Richard Barber's The Holy Grail: Imagination and Belief which unfortunately was published too late for us to use for The Da Vinci Hoax. This is a good survey of the legends down to their modern applications, including Holy Blood, Holy Grail, which rates a guffaw. Barber firmly sets the medieval romances within the Church's teachings on the Holy Eucharist. This would be an excellent place to become acquainted with the authentic stories. Then you might want to read the most spiritual of these, The Quest of the Holy Grail, translated by P.M. Matarasso and available as a Penguin paperback. If you do read it, you'll be ahead of Dan Brown whose deep and profound research didn't extend to studying any medieval sources.