That's good news, I have read all of the books in this series, and I'm finishing the 2nd last one
"Sword of Kings" right now, with a couple of chapter to go, should be finished this weekend.
On Bernard Cornwell's website it states
"My next book ‘War Lord’, the thirteenth book of The Last Kingdom series, will be published in the UK on 15 October 2020."
It seems that his publishers always makes sure the latest book is released in time for Christmas, so now my daughter has my Christmas present organised