[Photo by: Warner Bros. Records/YouTube]

At her show in San Diego last night, Halsey brought out Andrew McMahon to perform Jack's Mannequin's "Dark Blue," and we're truly feeling all the emotions.

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"Dark Blue" is taken from Jack's Mannequin's 2005 record Everything In Transit, and it's clear that Halsey is as big of a Jack's Mannequin fan as we are.

Watch footage from their live performance below:

Understandably, fans are loving their live collaboration:

And McMahon shared a photo, thanking Halsey for the opportunity. "You and your band put on an amazing show and I was honored to share the stage."

It truly is a collab we could only dream of—we just wish we were there to see it live!

What are your thoughts on their performance? Let us know in the comments below!

Watch more: APMAs 2017 Performance: ANDREW MCMAHON