OMG

omg i almost forgot! brisingr came out! *whoot* i <3 that series!

but i haven't read it yet. and the suspense is killing me! i want eragon to find out that brom was his father. and yes i am 99% sure that this is true even though it hasn't been written in the book. well technically it has... at least some clues. =P okay dont read the part below if u want to figure this out for yourself.

The True Identity of Eragon’s Father
Okay so you might think that since Murtagh said that Morzan was Eragon’s father in the ancient language, and you can’t lie in the ancient language, Morzan must be his father. However, this is not at all true, and in reality Morzan is not Eragon’s father. It is Brom.

First, you must understand that it is possible to tell an untruth in the ancient language. You see, just because Murtagh said it in the ancient language doesn't mean that it's true, just that he believed it was true. When Eragon wrote a poem for the Agaeti Blodhren we learned that it is possible to “lie” in the ancient language. Oromis said it was possible to tell untruths in the ancient language, if you really believed that they were true. Here’s the proof.

Eldest Pg. 456
“No barrier exists to writing fiction in the ancient language. The difficulty arises when one attempts to speak it, for that would require you to tell untruths, which the magic will not allow.” “I can say it,” replied Eragon, “because I believe it’s true.”

So because Murtagh has seen no evidence showing that Eragon could not also be a son of Morzan, and because they do share a mother, he believes that Eragon was also the son of Morzan.

Now evidence about Brom being Eragon’s father…

Eldest Pg. 546
"Son and Father alike, both blind as bats".
Blagden never met Morzan so he could not have been talking about him. Morzan was never blind. He knew exactly what he was doing. He was after power. Brom was the only one who was blind by his insane idolization of Morzan. Brom was blind to Morzan's betrayal, and Eragon was blind to Murtagh's betrayal.

More evidence…

Eldest Pg. 546
"While two may share two,
And one of two is certainly one,
One might be two."

While two sons (Eragon and Murtagh) "may" share the same two parents (Morzan and Selena),
And one parent of two parents, the Mother-Selena, is certainly the same one parent of both sons, One parent, the Father, might be two Fathers (Brom and Morzan) each having one of the sons.

What in the world could this riddle be about if it doesn't support the two-father theory?

There is a chapter in Eldest titled "Inheritance." In it, Murtagh takes Zar'roc from Eragon and claims it as his inheritance. This conveniently leaves Eragon without a sword. In the third book Eragon will get his inheritance and his proper rider's sword (meaning that it matches the color of his dragon). Brom’s sword will be blue because he also had a dragon named Saphira.
We are never told what happens to Brom's sword. It is only mentioned indirectly when Eragon converses with the elf sword maker Rhunon. She mentions that there are only two of her swords left (other than Morzan's and Oromis'), and they happen to each be held by two elven families. One is Brom's, and the other is likely another sword that will go to the rider of the other dragon in Galbatorix’s possession. And don’t you dare think that Rhunon will make Eragon’s sword because she sworn in the ancient language to never make another rider’s sword again. This makes Brom’s sword Eragon’s inheritance, and this is the Inheritance Trilogy, after all.
However, there are some other questions that must still be answered. For example, why, if Brom was Eragon’s father, would he not raise his own son while both live in Carvahall? And why would Brom never tell Eragon that he was his father?
In response to those two questions: there was no evidence whatsoever to imply that Eragon would be a rider in his early life. Brom was there in Carvahall to watch over him, and he did teach his son all about the old ways. When Eragon went to Brom's to ask him questions about the riders Brom answered all of his questions and he often told stories to him. One of the best ways to teach is through stories, and in order to have Eragon learn more he had to be interested in riders and their history. In Eragon, it says that Brom has been living in Carvahall for 15 years, Eragon’s age in that book. (Hmmmm… suspicious…)

If Eragon knew that Brom was his father, he could possibly reveal it when someone enters his head (like the Twins.) If Galbatorix found out that the newest rider that wasn't under his control was the son of Brom, he would have to assume that he was raised by Brom, and was the beneficiary of a lifetime of teaching by Brom. Since we know Brom was powerful and strong enough to have a hand in the deaths of eight of the Forsworn, his lifetime knowledge passed down to his son would make Eragon a much more deadly enemy than if Eragon was raised by a random farmer and never had any contact with Brom. If Galbatorix believed that Eragon was Brom's son, he himself would have flown to the battle at the end of Eldest, and it would have been a forgone conclusion.

And if Brom is indeed Eragon’s father, then how on earth would he and Selena have a chance to "make" Eragon? =P

We don’t know exactly how long Selena was missing from the castle ("many months" is a very unclear length of time.) She could have met Brom and fallen in love with him after running from the castle. Bear in mind that around the time of Selena’s disappearance, Morzan was off searching for Saphira’s egg, which had just been stolen, so would not have been around the castle or seeing Selena at any time. And that give Brom ample opportunity to see her. Brom also tells Eragon that he knew Selena (which Eragon never knew before) “well enough to miss her when she’s gone.”

haha see? i told u he was Eragon's father. xP or at least he better be...