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 "Al Jolson"): Al Jolson (born Asa Yoelson; May 26, 1886 – October 23, 1950) was an American singer, film actor, and comedian.
Relevant evidence: Yes