Stan Lee Reveals He's Fighting Pneumonia

Stan Lee's finally revealing why he's had to bail on his throngs of Marvel Universe fans lately -- the comic book legend is fighting pneumonia like Spidey fights crime.

The Marvel co-creator recorded a personal message filmed by his friend and filmmaker, Keya Morgan, to update everyone on his health. You can tell the normally energetic 95-year-old is having a tough time ... but he reassures fans he is getting better.

As we reported ... Stan has been dealing with a string of issues besides his lungs recently -- from missing money, to a face-off with his former body guard and a heart health scare.

On the flip side, the "Black Panther" box office has gotta make him smile. As Stan puts it ... "Excelsior!"