The duo performed Get Back during MCCartney's lengthy encore at the Chicago music festival, reports.

The Fab Four legend later tweeted on Saturday (01Aug15), "Thank you Chicago! Thank you #Lollapalooza! And thank you Brittany Howard! #OutThere #alabamashakes #Lolla2015".

The two-hour set overran, much to the delight of the crowd, and featured plenty of Beatles and Wings classics. MCCartney also teased fans with a snippet of his hit with Rihanna and Kanye West, FourFiveSeconds - it is the first time he's performed the song solo, since the trio debuted it at the Grammy Awards earlier this year (15).