this clip of him playing a couple of numbers with Bruce Springsteen at the end of the latter's show in Hyde Park last year.
What I was really looking at was the grin all over Springsteen's face, a grin which clearly announces "Look! I know I'm an immense star in my own right but this is different because I'm singing with a Beatle!"
If you're under fifty all rock stars who made their name before you were born probably merge into the same pantheon. If you're from Springsteen's generation, who sat as teenagers and gawped at the The Beatles on Sunday Night At The London Palladium or The Ed Sullivan Show, then whatever stardom you happen to achieve in your life will always be nothing more than a base camp compared to the Everest that is Beatles fame.
This doesn't just apply to rock stars, who instinctively defer whenever a Beatle or a Stone heave into view. We all feel versions of the same thing. You can never be truly, knocked-sideways impressed by meeting people unless they were big stars when you were young. That's the point, when you were a child and they were just a few years ahead, at which you establish a way of looking at the world which never really changes.