James has an all-star backing band
James, 35, was gigging ahead of a 47-date tour in America later this year and had asked Rolling Stones rocker Ronnie, 65, to play guitar with him on stage.
Sir Paul, 70, watched from the wings at the Ambassadors Theatre but appeared in front of the crowd to jam on the piano during one tune.
James – whose mum was the late Linda McCartney – is thought to have been encouraged to step out of Sir Paul‘s shadow and focus on his music by stepmother Nancy Shevell.
But it seems he’s got a little way to go before he reaches his dad’s height of fame.
Both Sir Paul and Ronnie were mobbed by fans as they left the venue, while James managed to escape with ease alongside sister Stella.