A plaque in Belfast City Hospital marking the formal opening of its tower block by Prince Andrew has been removed.
The Belfast Trust said the display was removed without its direction and its whereabouts are "currently unknown".
The Duke of York officially opened the Belfast City Hospital tower in June 1986.
A plaque marking the occasion was situated near the front entrance to the hospital.
It read: "Belfast City Hospital tower opened by HRH the Prince Andrew, 25th June 1986."
The display is believed to have been removed in recent days.
In a statement a Belfast Trust spokesman said: "A plaque near the entrance of Belfast City Hospital has been removed without any direction from Belfast Trust.
"Its whereabouts are currently unknown."
It comes as Prince Andrew faces civil action in the US over sexual assault allegations.
He is being sued by Virginia Giuffre, who claims he abused her in 2001 when she was 17. Prince Andrew denies the allegations.
The Duke of York's military titles and royal patronages were earlier this month returned to the Queen.
Meanwhile, the DUP has reversed its position on calls to no longer fly the Union flag at Belfast City Hall to mark Prince Andrew's birthday.
An SDLP proposal to not fly the flag on February 19 was backed by Sinn Féin and Alliance at a Belfast City Council committee meeting last Friday.
The move is expected to be ratified at full council next month.
DUP councillors voted against. The party's group leader Brian Kingston had said the council should continue to follow the UK government's list of designated days which include Prince Andrew's birthday.
“We are certainly not blind to the allegations of gross misconduct, and we share the deep concern about these. But we should await the outcome of the trial," he said.
But on Monday Mr Kingston told BBC Talkback they would accept an alternative day of flying the Union flag on July 1 to mark the Somme.
Mr Kingston said: "Yes we would support that, and we would seek that assurance that this would be a permanent arrangement.
"Obviously we have our own wreath-laying on July 1 annually already, so it would be quite appropriate as with Remembrance Sunday that we had the Union flag flying that day."
Belfast City Hall has flown the flag on designated says since a vote in December 2012 to end its permanent display.
The decision sparked weeks of street protests and disruption as loyalists clashed with police.
The Alliance Party has written to the UK government asking it to remove the Duke's birthday from the list of designated days.
