I'm sorry he didn't make it.
I don't think it was velvet or brook that killed him, even though they can't be ruled out. I'm pretty sure it was either the Cryptocaryon or a secondary bacterial infection.
In the first picture he had already a very heavy Cryptocaryon infection. Every white dot you see on him you have to multiply with 200 to 300 to get the intensity of the next wave that will hit him. Assuming he had about 500 parasites on his skin, fins and gills and taking the high multiplier of 300 you get 150,000 tomites for the next wave. That's absolutely lethal.
While Cryptocaryon builds up slow in the beginning it can progress quickly at advanced stages as it has an avalanche effect to it. When you see a fish having more white dots than you can easily count immediate action is required, even if it is just one transfer right after the parasites fall off to reduce the intensity of the next wave. Switching to therapeutic Hyposalinity is another way to at a minimum give the fish some relive and to buy some time until you can set up everything for TTM. In many cases hyposalinity alone may even be enough to kill the parasites off. Though it would still be a good idea to do a round of tank transfers to be on the safe side.