Inappropriate elimination can be caused by a range of issues. Medical issues can including, diarrhea, constipation, IBD, dietary intolerance or food allergies, intestinal parasites, pain while squatting, etc. There are also a range of behavioral and management issues including stress or anxiety, infrequent cleaning of the litter box, dislike for the type of litter or type of box, dislike for location of the box, etc.
I would recommend that Teddy be examined by a vet for a potential medical issue. The vet may also be able to pinpoint what changes could have happened at home that caused Teddy to stop using the litter box. Until you see the vet, you may set up a second litter box in a new location to see if he prefers that.
Here is some more information you may find useful:
http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=88http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=3638http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=1470