I think I'd explore where the new growth is to find whether it's from the root or from the Contender. If it's from the root you probably wouldn't want its peaches. You might use it to graft another peach variety to. If it's from the Contender you would want to keep that. It's going to make a full size peach tree which is not big compared to a full size apple tree. If the growth is from the root I'd consider grafting a piece from the Contender to the rootstock and possibly save the tree.

Google "whip and tongue graft" or "T bud grafting" to get an idea of what's involved. The whip and tongue is usually done in late winter on dormant stock. The T bud is usually done in late July or early August. I've successfully done the whip and tongue but never got a T Bud to survive.

I tried to identify it by following it down with my finger. I think it is part of Contender. I cannot be certain. Below the soil line it curves to toward the old trunk. So, I cut down the tree, and kept this fledgling. I willl see what develops.