The 37-year old man leapt over the chest-high barrier and landed in the water trench on Monday morning and simply ignored the zookeepers who tried to convince him to climb back out.
While Knut - raised by humans as cub - didn't seem to be bothered by the surprise guest, police managed to get the reluctant zoo visitor out of the enclosure while the bear was distracted, the paper reported.
Though Knut's early experiences make him unnaturally friendly to humans, the two-year-old bear now weighs more than 200 kilogrammes, stands nearly 2.5 metres tall and could easily kill someone. The Knut fan will now face charges for breach of the bear's domestic peace.
Though he's been a money-maker for the Berlin zoo, the lucrative bear might have to leave his home next year. He is owned by the Neumünster Zoo in Schleswig-Holstein, which will decide on his new home, even though Berlin wants to keep its furry celebrity.
More than five million people have visited Knut since his world premiere in March 2007 and brought more than €5 million from Knut-based souvenir and ticket sales into the empty tills at Berlin zoo.