Question: John Sebastian is an American-born singer-songwriter, guitarist, harmonicist, and autoharpist,  best known as a founder of The Lovin' Spoonful, that did an impromptu appearance where in 1969? 
Sentence (from "John Sebastian (classical harmonica player)"): John Sebastian, born John Sebastian Pugliese (April 25, 1914 − August 18, 1980), was an American musician and composer known as a master of the classical chromatic harmonica.
Relevant evidence: No