Harpo Marx, who was plugging his new book, appeared on I’ve Got a Secret, 1961. Johnny Carson on the panel.

From the 1983 New York Times obituary of Mildred Dilling, who taught Harpo how to play his musical instrument and was profiled in the New Yorker in 1940 (subscription required):

“Mildred Dilling, a concert harpist who performed for five Presidents, taught Harpo Marx and owned the world’s largest private collection of harps, died in her Manhattan home last Thursday. She was 88 years old.

Miss Dilling performed throughout North and South America, the Orient and Europe. At the peak of her career, she gave 85 concerts and traveled 30,000 miles a year. In her early 80’s, Miss Dilling was still performing 10 concerts a year. She also conducted harp workshops at colleges and universities, giving master classes at the University of California, Los Angeles.”