"Three things cannot be long hidden. The Sun, the moon and the truth." 


A FACT is something that has really occurred or is actually the case. The usual test for a statement of fact is verifiability, that is whether it can be proven to correspond to experience.

Truth is most often used to mean being in accord with fact or reality, or fidelity to an original or to a standard or ideal.The commonly understood opposite of truth is falsehood.

An opinion is a judgment, viewpoint, or statement about matters commonly considered to be subjective, i.e. based on that which is less than absolutely certain, and is the result of emotion or interpretation of facts. 

*See Wikipedia for more on Fact, Truth and Opinion.