The Duke and Duchess of Sussex made a special visit to New York's One World Trade Centre on Thursday.
The couple posed for photographs at the top of the skyscraper against a panoramic backdrop.
Mr de Blasio's wife, the first lady of New York, writer and activist Chirlane McCray, and their son Dante de Blasio also joined the group.
Asked by a reporter if they were enjoying their trip to New York, Meghan, dressed in a black high-necked coat and black trousers, smiled and replied: "It's wonderful to be back, thank you."
The visit is the couple's first public appearance together since the birth of their daughter Lilibet in June.
One World Trade Centre has been built on the site of the original twin towers.
Their visit comes just two weeks after the 20th anniversary of the September 11 attacks.
Prince Harry and Meghan remembered the anniversary and transformed their website Archwell to mark the milestone.
Archewell’s homepage had a black drop with the words “In Memoriam, September 11, 2001” at the top.
The Sussexes are in New York to take part in a worldwide event on Saturday urging leaders to adopt a vaccine equity policy to help end the Covid-19 pandemic.
They are joining the 24-hour broadcast Global Citizen Live being staged in New York's famous Central Park and around the world.
It is part of a number of shows being held in cities as varied as London to Lagos by the organisation Global Citizen, with artists like Ed Sheeran, Sir Elton John, Kylie Minogue, Metallica and Coldplay scheduled to perform.