Originally Posted by Evita
He says he doesn't know anything -- and I believe him He certainly fooled Tom too

Roth's inside man Fredo's own words, lie after lie, he was feeding Michael
1. I haven't got a lot to say Mike.
2. I was kept pretty much in the dark.
3. I didn't know all that much.

Let's stretch what was seen onscreen and give him the benefit of the doubt that Roth misled him, he really thought his little help to close the deal fast -- in Roth's favor against his own brother for “something in it for me -- on my own” would be good for the family and he didn't know it was gonna be a hit

If that's all it was,
1. why bring up the Donship?
2. Why would the Donship be even an issue?
Exactly Evita why mention the Donship at all unless “something in it for me -- on my own” was, the Donship and the only way this could happen is if the current Don, Michael was dead or in prison

Why would the Donship be even an issue?
Sure thing if Fredo hadn't mentioned the Donship, we can try and stretch the truth as unconvincing! as it is....

However we can't ignore all the mounting evidence pointing to Fredo indeed set out to harm and injure his brother Michael, for the Donship and the fact remains “He betrayed his brother for personal gain”