Knut the celebrity polar bear must be castrated, say animal rights activists.
The bear, which became such a huge star that he graced the cover of Vanity Fair, has been introduced to Giovanna, a lively female.
Since then visitors to Berlin Zoo have been treated to a daily spectacle of the two playing together and looking like they are loving every minute of it.
However, the German branch of the animal rights group, People for the Ethical Treatment of Animals, insisted that as the two bears shared the same grand-father, their future offspring and the future of captive polar bears in general was at serious risk through the possibility of inbreeding.
"Knut fans should be aware that only Knut's castration would allow the long-term cohabitation of Giovanna and Knut," insisted Frank Albrecht, PETA's zoo expert with more than a hint of schadenfreude.
"All other hopes and desires would bring the polar bear population in captivity to its pre-programmed demise even more rapidly," he added.
The suggestion has caused howls of protest in Germany.
Berlin's Knut fan club has been campaigning vigorously for Giovanna to stay on in Berlin as the two bears have adapted well to each other.
Since his birth in 2006 to a maltreated circus bear who subsequently abandoned him, Knut has earned well in excess of €10m for the zoo. Millions of Knut cuddly toys, based on what he looked like as a cub, have been sold.