The members of the Austin High School band weren't the only ones making a cameo during Mumford & Sons' closing set on Sunday night at the Austin City Limits Festival.

Metallica co-founder and drummer Lars Ulrich made a surprise appearance with Marcus Mumford & co. for their hit song "The Wolf," one year after headling ACL Festival with his own band.

"So [expletive] cool to share the stage with Mumford & Sons and bash away on their awesome song The Wolf at ACL last night. Thank you for encouraging me to come up and [expletive] rock with you... Fun times fellas!" he said of the experience in an instagram post.

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So fucking cool to share the stage with Mumford & Sons and bash away on their awesome song The Wolf at ACL last night. Thank you for encouraging me to come up and fuckin rock with you.... Fun times fellas! #wanna #aclfest

A post shared by Lars Ulrich (@larsulrich) onOct 14, 2019 at 5:09pm PDT

Ulrich also watched (but didn't perform in) Guns N' Roses set from backstage on Friday night.

"Look ma'...best in the [expletive] house!!! Great to connect again with friends from back in the day who are rockin harder than ever...beyond next level!" he said of Guns N' Roses' show.

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Look ma’.....best seat in the fuckin house!!! Great to connect again with friends from back in the day who are rockin harder than ever...beyond next level! #wanna

A post shared by Lars Ulrich (@larsulrich) onOct 11, 2019 at 9:56pm PDT

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