While it's not a set premiere date YET, HBO did confirm that the 8th and final season of Game of Thrones will be premiering sometime in April 2019.
There was also this video:
— Game Of Thrones (@GameOfThrones) November 13, 2018
And this set of #ForTheThrone images shared by the official Game of Thrones twitter account:
We'll of course let you know when we get an actual premiere date, we're expecting it to be the 21st of April.