The National Portrait Gallery will not reopen its doors until 2023.
The Gallery, currently closed because of the pandemic, had hoped to welcome back visitors before it was due to close on June 29 as part of a £35.5 million redevelopment project.
But it said it will now remain shut throughout June “to help contain the spread of the virus and ensure the safety of visitors and staff”.
National Portrait Gallery director Nicholas Cullinan said: “We had very much hoped we would be able to reopen the Gallery to visitors before our refurbishment commenced, but sadly it is now clear that this won’t be possible.
“We understand how disappointing this will be for many people who had planned to visit the Gallery for a final time”.
The Gallery, near Trafalgar Square, will reopen in spring 2023.
It will loan hundreds of works from its collection during the period of closure.
David Hockney: Drawing From Life, which was on display when it had to close, will be staged again when the Gallery reopens.
The exhibition Cecil Beaton’s Bright Young Things, which was due to end in June, will tour.
The transformation of the Gallery will be the biggest since it opened its doors in 1896.
It plans to create a new main entrance, “bring back to life” its East Wing and create a public forecourt.
It will also redisplay all of the collection in its 40 galleries, providing a “greater and more diverse selection of portraits”.