Simpson and Lachey in awkward moment

Nick Lachey's awkward prize at the Jessica Simpson-hosted Teen Choice Awards turned even more uncomfortable backstage when a chance encounter saw his ex-wife allegedly "freak out".

Lachey picked up the award for Best Love Song on Sunday, written about his break-up with Simpson, and the couple desperately tried to avoid an uncomfortable encounter during the ceremony.

However, a witness tells American publication Us Weekly the two accidentally bumped into each other backstage, remarking: "They looked at each other, then Nick looked away and kept walking.

"Jessica freaked out, though and (friend and hairstylist) Ken Paves started fanning her."