You're not gonna believe this one...

UK jazz superstar JAMIE CULLUM has been jamming with N.E.R.D, NME.COM can reveal.

The unlikely collaboration came about at the South By South West music convention in the US. The crooner appeared on stage during N.E.R.D‘s show at the Austin Music Hall (March 20).

A fan at the gig told NME.COM:” Jamie played his own show at midnight on the 18th floor of the Crowne Plaza, then hopped in a cab and raced across town to sing ‘Frontin’’ with N.E.R.D.

“Pharrell Williams went on about how cool he was and talked about how he hoped to work with Jamie in the near future.”