Embed YouTube videos in WordPress – remove related videos
If you upload videos to YouTube before embedding them in your WordPress blog you may want to remove the related videos that display automatically when you get to the end of the video. This can be done by typing ?rel=0 directly after the URL eg http://YouTube.be/M_f4u4rWXHA?rel=0
For the ?rel=0 to work properly you do need to activate the JetPack “Shortcodes Embed”.