The official Amazon release date is June 8th! The release date for Nook, Kobo, iBooks and Smashwords is June 6th, On June 6th at 12pm GMT it will be taken down from those platforms in order to be enrolled in Kindle Unlimited.
If you do not purchase from Amazon PLEASE be sure to pre-order your book before it is gone. It will ONLY be available on Nook, Kobo, iBooks and Smashwords until 12pm GMT on June 6th. After that you will only be able to purchase it from Amazon for at least 3 months.