Can Dumbledore be half-blood?

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I've been reading Mugglenet's guide to what may happen in Book 7 (I know it's pretty late, but I got a bit upset last night and I was in front of a bookstore so I bought this. lol! Anything Harry Potter is relaxing to me). I just realized that the powerful wizards in the series are mostly half-bloods. In the book, they made a pretty convincing argument that Snape may well be the third most powerful wizard in the world. Of course, Dumbledore is #1, and then Voldemort. Snape can fool Voldemort with his Occlumency even though Voldermort is said to be the best Legilimens in the world. He's also said to be the only one who can brew potions that can help Dumbledore heal the nasty effects of the Horcrux ring. And as every Death Eater that broke away from Voldemort (like Igor Karkarof and Regulus Black), they didn't last very long until the got killed. Assuming that Snape is really on Dumbledore's side, making the Dark Lord believe that he is still on his side is a very remarkable ability. Anyway, to the question. Voldemort is half-blood, even though he tried his best to disassociate himself from all his muggle ties. Snape is proud to be a half-blood. He's the half-blood Prince! They are two of the most powerful wizards... So do you think Dumbledore could also be half-blood? We've seen some Muggleborn and half-bloods excel in the books. A perfect example is Hermione. I really can't remember if Dumbledore's lineage was mentioned in the books... Help me out!!! :)