Three Prisoners and King Logic Riddle

Once a King came to prison with a bag and showed it to the three prisoners . The bag had 5 discs in it. Three White and two black.

 Then he tells them to turn around and sticks one disc at back of each prisoner and leaves with rest of the discs in bag WITHOUT showing them to any of the prisoners. Now each prisoner can see the disc at back of other two prisoners but not the one at his own back. They are not allowed to speak.

The one who will tell the guard sitting outside the prison about the color of the disc stuck on his own back would be released. After some 30 minutes one of the prisoner, on seeing that other two prisoners have white colored discs on their back comes out and tells the color of disc at his back with the logic.

He was released..What does he says ? You have to tell what logic did the released prisoner gave and what was color of disc on his back?

Hint: Think about what other prisoners would have been thinking and what could be the possible cases?

Video Asking The Logical Puzzle:

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Solution to Logical Puzzle King and Three Prisoners