Marius van der Westhuizen has been stood down from assistant refereeing duties for Ireland's Grand Slam clash, after attending an England training session.
Global governing body World Rugby has replaced Van der Westhuizen with Wales' Nigel Owens - and accepted full responsibility for what it branded an "oversight".
South African official Van der Westhuizen refereed England's training session at their training headquarters on Tuesday, just four days before he was due to run the line when Ireland face Eddie Jones' side at Twickenham.
Ireland boss Joe Schmidt had on Thursday lunchtime insisted he had faith in Van der Westhuizen's "integrity", but now any possible conflict of interest has been removed.
"World Rugby has confirmed that Marius van der Westhuizen will be replaced by Nigel Owens as assistant referee 2 for the NatWest 6 Nations match between England and Ireland at Twickenham on Saturday," World Rugby announced.