Lucy Meets the Mustache (1960) was not only the last show of the series, it was the very last acting of the quartet (two actresses & two actors), Lucille Ball, Desi Arnaz, William Frawley Vivian Vance. Vivian Vance did not want any more acting with William Frawley, even though there was a contract offer of "The Mertz Apartments" to see how guest star celebrities would be treated, in their apartment room(s).
After The Lucy-Desi Comedy Hour (1957) concluded filming this finale, Lucille Ball immediately filed for a divorce from husband, Desi Arnaz.
After the dinner party, Ethel says to Fred "Goodnight, Bing," when he leaves the Ricardo home to go to sleep. This is, of course, an allusion to popular singer Bing Crosby.