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.
"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."
The Irish camp had made a measured response to the issue of Van derWesthuizen's position on Thursday, with boss Schmidt insisting he was relaxed about the South African's role in Saturday's crucial encounter.
"That is a bit of a surprise," said Schmidt, of Van der Westhuizen helping out at England training this week.
"I'm sure in retrospect people are probably thinking it's not the best thing to do.
"I know Marius and I would have no hesitation in standing by his integrity.
"I don't think it will affect his decision-making and we'll stand by him as an official on Saturday."
England boss Eddie Jones had also earlier insisted Van der Westhuizen's neutrality should not be in question.
"What, are you questioning his integrity?" asked Jones, when asked about the issue.
"We went through World Rugby, which is the proper channels, so you are asking the wrong person."