Bill Watterson, creator of the long-defunct Calvin and Hobbes comic strip, says he made a brief, unannounced return to newspaper cartooning to raise money for a good cause - and because he thought it would be funny.
Watterson collaborated with Pearls Before Swine cartoonist Stephan Pastis on three strips that ran last week.
The strips made fun of Pastis' drawing ability, and Watterson drew one panel in each.
It was the first time his art has appeared in the funnies since Calvin and Hobbes ended its run in 1995.
The reclusive Watterson, who lives in Ohio, told The Washington Post that he joined up with Pastis to raise money for Team Cul de Sac, a charity co-founded by cartoonist Richard Thompson that raises money to fight Parkinson's disease. Thompson suffers from Parkinson's.
"Several years ago, when Stephan did one of his strips that mocked his own drawing ability and mentioned my strip in comparison, I thought it might be funny for me to ghost Pearls sometime, just to flip it all on its head," Watterson said.
"It was just a silly idea, and I didn't know Stephan, so I never pursued it, and years went by."
Then the idea resurfaced.
"I thought maybe Stephan and I could do this goofy collaboration and then use the result to raise money for Parkinson's research in honour of Richard Thompson. It just seemed like a perfect convergence."
Pastis paid tribute to the final Calvin and Hobbes strip in Saturday's panels.
The original Pearls Before Swine strips featuring Watterson's work will be auctioned off for Team Cul de Sac.
Pastis said he never expected even to speak to Watterson. Working with him, he said, "is like getting a call from Bigfoot".