There are other possibilities, but this is most likely cedar apple rust, a common and widespread fungal infection on apples. It gets its name from the fact that the fungus overwinters on cedars, then infects the leaves, twigs and fruit of the apples. Spraying with a fungicide at the proper time is really the only practical means of dealing with the infection. It is probably too late for that this year. Removal of nearby cedars can help, but is not usually a realistic possibility.

there is a very active fruit forum ... they do things a lot different that tree peeps ..

and the most important.. is the 3 to 5 spraying PER YEAR .. to grow pretty fruit ..

frankly.. i gave up on fruit a long time ago ... because it wasnt worth the effort ...

there is nothing you can do ... to make what fruit you have pretty.. this year ... though you may still get some apples for a pie or 3 ... presuming of course.. they are good apples ... you still dont know that ...

unless you want to invest considerable time and effort in fruit growing.. consider removal of the tree ... its ok, if you want to ...

fruit peeps also do significant annual pruning.. to reduce the crop size.. and to open the tree up to get sun inside .. another annual maintenance .. resulting in a nice crop.. but a potentially ugly tree ... walk thru any local orchard ... and see what i mean ...

its a great hobby.. if you want to invest the time.. effort and money ... but many of us.. chucked that hobby long ago ...

ken