Your Grace's displeasure and my imprisonment are things so strange unto me, that what to write, or what to excuse, I am altogether ignorant. Whereas you send unto me (willing me to confess a truth and so obtain your favour), by such a one, whom you know to be mine ancient professed enemy, I no sooner received this message by him, than I rightly conceived your meaning; and if, as you say, confessing a truth indeed may procure my safety, I shall with all willingness and duty, perform your duty. But let not Your Grace ever imagine that your poor wife will be brought to acknowledge a fault, where not so much as a thought ever proceeded. And to speak a truth, never a prince had wife more loyal in all duty, and in all true affection, than you have ever found in Anne Bulen - with which name and place I could willingly have contented myself, if God and your grace's pleasure had been so pleased. Neither did I at any time so far forget myself in my exaltation or received queenship, but that I always looked for such alteration as I now find; for the ground of my preferment being on no surer foundation than your Grace's fancy, the least alteration was fit and sufficient (I knew) to draw that fancy to some other subject.
You have chosen me from low estate to be your queen and companion, far beyond my desert or desire; if, then, you found me worthy of such honour, good your Grace, let not any light fancy or bad counsel of my enemies withdraw your princely favour from me; neither let that stain - that unworthy stain - of a disloyal heart towards your good grace ever cast so foul a blot on me, and on the infant princess your daughter.
Try me, good King, but let me have a lawful trial, and let not my sworn enemies sit as my accusers and as my judges; yea, let me receive an open trial, for my truth shall fear no open shame. Then you shall see either my innocency cleared, your suspicions and conscience satisfied, the ignominy and slander of the world stopped, or my guilt openly declared. So that, whatever God and you may determine of, your Grace may be freed from an open censure; and my offense being so lawfully proved, your Grace may be at liberty, both before God and man, not only to execute worthy punishment on me as an unfaithful wife but to follow your affection already settled on that party for whose sake I am now as I am, whose name I could some while since have pointed unto - your Grace being not ignorant of my suspicions therein.
But if you have already determined of me, and that not only my death, but an infamous slander must bring your the joying of your desired happiness, then I desire of God that He will pardon your great sin herein, and likewise my enemies, the instruments thereof; and that He will not call you to a strait account for your unprincely and cruel usage of me at His general judgment seat, where both you and myself must shortly appear; and in whose just judgment, I doubt not (whatsoever the world may think of me), mine innocency shall be openly known and sufficiently cleared.
My last and only request shall be, that myself only bear the burden of your Grace's displeasure, and that it may not touch the innocent souls of those poor gentlemen, whom, as I understand, are likewise in strait imprisonment for my sake. If ever I have found favour in your sight - if ever the name of Anne Bulen have been pleasing in your ears - then let me obtain this request; and so I will leave to trouble your grace any further, with mine earnest prayer to the Trinity to have your grace in his good keeping, and to direct you in all your actions.
From my doleful prison in the Tower, the 6th May. Your most loyal and ever-faithful wife, Anne Bulen
For several reasons which include, from The Anne Boleyn Files --
Read more: http://www.theanneboleynfiles.com/6-may-1536-from-the-lady-in-the-tower/#ixzz2SfrzpbLO
Many believe that the letter was a forgery. However, a theory is that Cromwell copied her actual letter and was 'referring' to her when he titled her 'the lady in the tower' and 'Anne Bulen', where she would have called herself Anne the Queen. It is highly likely that Anne tried to send Henry one -- if not a hundred -- letters in her defense, none of which reached him and all of which were burned in the great English library fire of 1731. It's likely, to me, that if this letter was not genuine, it was based off of a letter that was. My favorite point in its defense written in the above linked post to The Anne Boleyn Files states: "Anne could be provocative when she wanted to be. It may have been a huge risk to take but perhaps she wanted this one opportunity to tell the King what she thought of him and his plot."
I highly recommend reading Gareth Russell's article about the mystery, here.