The pair were both in the Illinois city on Friday night (September 15) and appeared at the Five Roses venue where they made an unplanned performance.
As Billboard reports, Skrillex played a 90-minute DJ set, while Sheeran acted as his hypeman. You can watch fan-shot footage below.
The pair have been musically linked in the past, with in-the-studio photos showing them working with Usher and Diplo. However, no music has been released as yet.
Sheeran recently joined Canadian singer Shawn Mendes on stage for a surprise duet.
The 19-year-old Canadian singer was headlining Brooklyn’s Barclays Center in August when the ‘Shape Of You’ singer made his way on to the stage.
Sheeran sang the second verse of Mendes’ song ‘Mercy’ with the singer while wearing bright red shorts and a flannel shirt, as Billboard reports.
“That was just as crazy for me as it was for you guys,” Mendes announced when Sheeran waved goodbye and walked backstage.
Meanwhile, Skrillex officially rejoined his old emo band, From First To Last, earlier this year. The band changed their Twitter picture to a new photo featuring Moore in February, along with the caption: “2017 Vibes <3”. Their Twitter bio now also includes Skrillex’s handle.
The DJ previously told Alt Press at the Grammys: “I left the band, but I would say I’m not left anymore.”