I’d add a couple assumptions to what I wrote earlier.
If the doctor that doesn’t deserve the name (John Hurt) fits between the 8th and 9th and was the one that fought the time war, then it’s possible that he got as desperate as the other time lords during the war.
Wich would possibly mean that he was the one who came up with the plan to destroy all of existance to save the time lords, or at least he did nothing to stop it , thus betraying the name of the Doctor.
The doctor never made a secret of the fact that he was the one that locked the time war away, so that can hardly be the secret of what the nameless did.
I can imagine the 11th Doctor along with the 10th being the ones that lock Gallifrey away and stop the nameless.
So the 9th doctor knows that he will in the future be the one that condems all of his race.
That’s twisted enough methinks.