Gwen Stefani couldn't hold back her tears during Monday's final knockout round on 'The Voice' when 16-year-old Brayden Lape, a member of Blake Shelton's team, delivered an emotional performance of Brett Young's 'Mercy.'  Calling Brayden 'so sweet' and a 'natural,' Gwen explained the heartfelt reason behind her emotional reaction.  Let’s watch the video to see this touching moment...