David Letterman made a surprise cameo on The Tonight Show Starring Jimmy Fallon on Feb. 10, interrupting Fallon's monologue to welcome his longtime musical director Paul Shaffer and The World's Most Dangerous Band,

On Feb. 10, David Letterman stopped by “The Tonight Show Starring Jimmy Fallon” while his former bandleader, Paul Shaffer, and his World’s Most Dangerous Band filled in for the Roots. It marked Letterman’s first “Tonight Show” appearance since Johnny Carson was host, back when the program still taped in Los Angeles.

John Oliver’s not the only talk show host who can drop in on another show unexpectedly. Last night, the great David Letterman made a rare appearance on the Tonight Show right in the middle of Jimmy Fallon’s monologue.