EXCLUSIVE

Johnny Fratto -- a fan favorite on "The Howard Stern Show" for years -- has died after a battle with lung cancer ... TMZ has learned.

Fratto passed away peacefully at 12:06 AM surrounded by family ... his wife Ivanka confirmed. He was 61.

Fratto was the son of famous mob boss Louis Fratto ...who was a major shot caller in Chicago, Illinois and Iowa in the '30s, '40s, '50s and '60s.

Besides appearing on Stern, Fratto ran several businesses -- including Beverly Hills Choppers.

On a personal note, we worked with Fratto for years -- and he was a good dude ... caring, genuine, honest.

R.I.P.