A few years ago I read an interview with Muhammad Ali in which
he said that Elvis briefly stayed at his Deer Lake training camp
during Ali's preparations for his fight with Joe Frazier. Ali
said that, at the time, no news leaked out that Elvis was there.
Apparently, Elvis stayed in the cabin with complete privacy.
Some may
doubt this story, but I did come across this excerpt from the London
Evening Standard ( "For Sale: The camp that made Ali great", 20th
December 2002, p63)

"the Deer Lake training camp [was] founded by Muhammad Ali 30 years
ago [where] Ali prepared for some of his greatest fights; and the
A-List of American society came to watch him and pay homage to a
legend-in-the-making. Rat packers Frank Sinatra and Sammy Davis Jnr,
artist Andy Warhol and famed sportscaster Howard Cosell were among
those who bunked down in the 18 cabins perched on the hillside. Elvis
Presley suddenly turned up at four o'clock one morning and Ali rose
specially to greet him, one 'king' sharing a pot of coffee with
Is Ali's claim that Elvis stayed in a cabin one
night without anyone else knowing about it true?