Then Jesus replied, “Have I not chosen you, the Twelve? Yet one of you is a devil!”
“devil” = diabolos = devil, false accuser, slanderer. “Metaphorically applied to a man who, by opposing the cause of God, may be said to act the part of the devil or to side with him.” (Strong’s)
Notice the emotion expressed by Jesus here. Those who reject Him grieve the heart of Christ, but those who wholeheartedly accept Him and what He says bring Him great pleasure and satisfaction.