Not conclusive but here are a couple of things I found online.
When Sir Donald Wolfit, the last of the great English actor/managers, was lying on his death bed, one of his young actors said to him:
"Sir Donald, after a life so filled with success and fame, dying must be hard..."
To which Sir Donald replied:
"Dying is easy....Comedy is hard."http://www.ohr.org.il/special/purim/laugh.htm
Suspiciously similar but with completely different names:
Being funny is not easy, as a joke told by Joan Collins in a recent Spectator column revealed. Apparently when the great actor Edward Kean was dying a young actor knelt by his side and whispered, "Sir, what is dying like?" "My boy," boomed the old thespian, "dying is easy - comedy is difficult".http://www.draytonbird.com/markart/ma20020131.asp
Hey, here's the column in question
As the venerable Edmund Kean lay on his deathbed, a young actor knelt by his side and whispered to him softly, ‘Sir, what is dying like?’ ‘My boy,’ boomed the old performer, ‘dying is easy — comedy is difficult.’
'Dying is easy, comedy is hard.'
Alan Swan (Peter O'Toole) quoting Edmund King in MY FAVORITE YEAR (1982)http://www.movies-quotes.com/FUNNY%20QU ... UGHTER.htm
Other attributions include Edmund Gwenn, David Garrick, Groucho Marx, Marcel Marceau, and of course Oscar Wilde.
Hmmm. Edmund Gwenn, Edmund King, Edward Kean... I sense a mutating meme here. I suspect this is one of those apocryphal things we'll never figure out. It probably really appears as a line in "My Favorite Year" but I know it didn't originate there.