So sorry to hear this sad news,i know what you must be feeling as i have also lost a cocker to bone cancer,she too,was ok till we went for a walk,then started to limp slightly,then i noticed a small lump coming on her leg joint,vets said it was athritis maybe,but then another lump came on her back leg,so they did a xray,found bone cancer every where which had advanced aggressively,and let her go whilst under.I knew deep down that it was bone cancer but you allways think there may be a miracle and it will be ok.She was 11,and my 2nd cocker,which was 25 years ago. Our thoughts are with you