The Blue singer was asked to step down from his assigned position in court when Judge Mary Jane Mowat recognised the 'All Rise' performer.
Judge Mowat asked the star "Don't I know you?" when he prepared to take a seat at Oxford Crown Court.
According to the Daily Mail, she announced: "I believe I know this gentleman," to which Ryan replied, "If you like music, you might have done. I haven't been to court or anything."
Judge Mowat then explained that rather than his numerous public appearances as part of Blue, she knew him from a pastime that they both share.
She replied: "I was thinking more about horses."
Ryan was then asked to stand down from the jury, who are hearing an assault case in a trial scheduled to last for three days.
He later revealed on Twitter that he was asked to stand down as he had purchased a horse from Judge Mowat.
Watch Blue's 'All Rise' video below: