The two Beatle bandmates took to the stage together for two songs during the encore, sending the surprised crowd into a frenzy.
Starr wasn't the only surprise guest. Joe Walsh, formerly of the Eagles, also took to the stage for the final performance of the night, leading McCartney to quip on Twitter "Meet the Beagles!"
McCartney was wrapping up his Freshen Up tour.
"I had a great night last night love you man peace and love," Starr wrote afterward on Instagram.
"The joy of playing with my Peace and Love brother!" McCartney wrote on Twitter.