Watch Slash and Chad Smith join Post Malone, Andrew Watt and Chris Chaney for an epic cover of Black Sabbath's War Pigs

Andrew Watt, Post Malone, Slash, Chad Smith. This eclectic group of musicians are bonded by two things: Ozzy Osbourne, and their love of jamming. Whether it's Watt and Posty's epic guitar battles or star-studded birthday jams with Rob Trujillo and Taylor Hawkins, one thing's for certain: they just can't resist the odd impromptu sesh.

To welcome in 2021, Post Malone invited both Slash and Smith to join him and his band – which included both Watt and Jane's Addiction bassist Chris Chaney – for an epic 10-minute version of Black Sabbath classic War Pigs at his New Years Eve’s Bud Light Seltzer Sessions Presents: New Years Eve 2021 Facebook livestream concert.

Before Slash's guest spot at the event – which was held at the MGM Resorts Las Vegas – Malone, Smith, Chaney and Watt performed a version of Alice In Chains’ Rooster, which can be viewed at the 34:53 mark below.

If you'll recall, Post Malone was one of many high-profile guests recruited by Andrew Watt during the recording of Ozzy Osbourne's latest album, Ordinary Man. 

Watt has been a fan of jams since a young age, telling Guitar World last month, "It’s always been my favorite thing to do. And over the past few years I've gotten to work with so many amazing people, and I've found a bunch of people in common that share the exact same passion as me of just wanting to play at any time, in any place, with anybody."

In the same interview, the producer also confirmed that he is halfway through work on Ozzy's new album, which is set to feature appearances from Smith, as well as Robert Trujillo and Taylor Hawkins.