We have a apple tree that has suddenly gotten real ugly. It has clumps of leaves all over it that are turning black and it is advancing
on the twigs and to branches. This tree has a history of fire blight that I always removed promptly, this does not look the same. On another tree that I found three spots, there was a reddish goo on two of the twigs.. this is starting with the leaves and advancing inward.
There may be other possibilities of fungal infection, but since you say your tree has a history of fire-blight, that is the most likely, an advanced fire-blight infection.
Blackening of the leaves and twigs and a "shepherds crook" bending of the branch tips are characteristic signs of early infection. At the early stage you can usually see the margins of the infections and prune out the infected tips a foot below the margins with healthy tissue. This is best done in the spring before infections advance.
As the infection progresses downward into the larger branches it can present as branch die-back. At that stage it is very difficult to eradicate without drastic crown reduction pruning, and it is difficult to determine where the margin of infection is, because it is more internal.