The supermodel and the 'No Fear' singer came out to support the up-and-coming designer as he showcased his Ground Control creations at Somerset House as part of London Fashion Week.
Kate was sat next to ex-boyfriend Jefferson Hack - father of her seven-year-old daughter Lila Grace - as James impressed the audience with the collection, which is described as "classic tailoring for the young man with a modern element".
Speaking of the show, he later told BANG Showbiz: "I was really pleased with it and just glad everyone made it."
Guests then went on to an exclusive PlayStation3 SingStar after party at Circus in nearby Covent Garden.
To celebrate his successful debut, James and his father got up and entertained the crowd with a version of David Bowie's 'Let's Dance' on the SingStar.