This is one party you can't miss. You're invited to celebrate Willie Nelson's 80th birthday with this week's CMT Hot 20 Countdown. Tune in as we share fun facts about the legend, along with birthday messages from his many famous friends and The Red Headed Stranger drops in for a visit. Also on the show, Brad Paisley takes a stroll down memory lane in "Beat This Summer." Find out where his latest video debuts on the countdown.