Question: What American singer, film actor and comedian, suddenly stood up during a performance of Gershwin's Liza (All the Clouds'll Roll Away) and started singing?  
Sentence (from "Liza (All the Clouds'll Roll Away)"): On the show's opening night in Boston on June 25, 1929, Keeler's husband and popular singer Al Jolson suddenly stood up from his seat in the third row and sang a chorus of the song, much to the surprise of the audience and Gershwin himself.
Relevant evidence: Yes