Imagine Robert Plant showing up to one of your gigs and joining you on stage...

Your cousin and his buddies got a rare treat indeed but I suspect this friendly conversation or talk happened before he found out his youngest son had died because that loss, understandably, devastated him and this is just MO, but I suspect his first marriage falling apart in the early 80's may have been connected to Karec's passing and subsequent grief. His closest friend in the band was John Bonham due to their shared working-class, Black Country roots and them being high-school friends. Bonham was also the only Zeppelin member to attend Karec's funeral afterwards. Again, after such a devastating loss, its a miracle Plant ever wanted to be a musician again or that Zeppelin recorded one more album or played further shows in U.K. or Europe again. After the 1977 tour ended, the band didn't see or hear from each other for almost a year-and-a half.
As I recall the photo of Robert and my cousin was taken two days before the report of his son’s death.
Yes, Bonham was Plant’s closest friend in the band having known him and worked with him since their Band of Joy days. Bonham was the one who convinced Plant to rejoin the band when initially felt he was done with the limelight.