My Cat Who Was Born In 2003, Is A Neutered

My cat who was born in 2003, is a neutered male cat. For the last week we have notices blood in his stool. He has been healthy all along and there is no chanvge in his behavior. The stool was analyzed by a vet, he has no parasites or eggs in his stool. The blood seems fresh and is in the last part of the stool. His stool is soft and he goes once or twice a day with fresh blood at the end of the stool. He has not been covering his stool with cat litter since this has happened.