This past weekend, Pearl Jam officially kicked off their massive 20th anniversary bash with a big party in Alpine Valley. This is the first official PJ20 event, with others showing the band screening a documentary directed by Cameron Crowe on the band's history at Toronto Film Festival, the band will also release their autobiography and soundtrack later this month. While at the big festival this past weekend, many surprises happened as Eddie Vedder joined The Strokes and Josh Homme of Queens of the Stone Age joined the band on stage, while the biggest and worst kept secret was Chris Cornell joined Pearl Jam for a long overdue Temple of the Dog reunion. Take a look at the videos below.