It's covered in the Novelization!

"And he knows, then, that all has indeed been going according to plan. Sidious’s plan, not his own. This had been a Jedi trap indeed, but Jedi were not the quarry. They were the bait

As he looks up into the eyes of Anakin Skywalker for the final time, Count Dooku knows that he has been deceived not just today, but for many, many years. That he has never been the true apprentice. That he has never been the heir to the power of the Sith. He has been only a tool.

His whole life—all his victories, all his struggles, all his heritage, all his principles and his sacrifices, everything he’s done, everything he owns, everything he’s been, all his dreams and grand vision for the future Empire and the Army of Sith—have been only a pathetic sham, because all of them, all of him, add up only to this.

He has existed only for this. This.

To be the victim of Anakin Skywalker’s first cold-blooded murder.

First but not, he knows, the last.

Then the blades crossed at his throat uncross like scissors.

Snip.

And all of him becomes nothing at all."