Many fans were pleased upon the surprise appearance of Neil Young during the set of headliner Paul McCartney. This happened during day two of Desert Trip, the Southern California rock festival catered to a more mature audience.

According to Rolling Stone, McCartney sang in front of 70,000 fans and performed a 7-minute medley of The Beatles's best songs. Upon Young's appearance, they performed the Lennon-McCartney duet "A Day In The Life." Neil Young's vocals added such a beautiful yet melancholy layer to the duo's version of the ballad.

The song then transitioned to "Give Peace A Chance."

Yahoo! reports this wasn't the first time the two rock legends joined forces, as they had done a performance together at Hyde Park in London.

Probably one of the highlights of their surprise duet is the special guitar solo done by Neil Young during "Why Don't We Do It On The Road?" It was a concert first, and the attendees said that it looked like it wasn't planned at all.

It was clear that the former Beatle was feeling nostalgic that night, as he performed many songs by the legendary band. He even performed "In Spite Of All The Danger," which was the first demo recorded by the British brand back in 1958.

He also performed a solo version of "FourFiveSeconds," which he originally performed with Kanye West and Rihanna.

Neil Young's appearance was his second during the festival, as he performed a full set earlier during the day. It's said that his performance was set on a "conceptual stage" with six massive Native American teepees adorning the stage.

He performed a lot of classic hits like "Heart of Gold" and "Down By The River." This song was said to be the main event of his set, and this segment alone lasted for 22 minutes.

Here's a video of the legendary duo performing "A Day In The Life" during day 2 of Desert Trip: