'Project Runway' Finalist Mychael Knight in Frail Condition at Last Fashion Show

"Project Runway" finalist Mychael Knight was still hard at work one month before his death, but an intestinal disorder was already taking a visible toll on his body.

TMZ obtained a video of Mychael at what's believed to be the last fashion show he attended ... on September 8 in NYC. While the beloved designer was posing with models ... irritable bowel syndrome left him looking incredibly fragile.

As we reported ... the season 3 sensation died Tuesday morning in a Georgia hospital where he'd been getting treatment for IBS ... which he said was destroying his immune system.

He was 39.