Marius Van der Westhuizen has been stood down from assistant refereeing duties for Ireland's Grand Slam clash on Saturday 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 Pennyhill Park on Tuesday, just five days before he was due to run the line when Ireland face Eddie Jones' side at Twickenham.
Ireland boss Joe Schmidt had earlier on Thursday 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," read a World Rugby statement.
"World Rugby takes responsibility for this oversight and has taken the proactive decision to stand Marius down to avoid any additional unfair and unnecessary conjecture. Marius is an outstanding talent with a big international future and both he and his employer SARU fully support the decision."