Prince William and Kate Middleton paid a somber visit to Ground Zero yesterday during the final day of their New York trip.

Torrential downpours didn’t stop the Duke and Duchess of Cambridge from paying their respects at the National September 11th Memorial and Museum in the morning. They laid a bouquet of white roses and a note, that read: “In sorrowful memory of those who died on 11th September, and in admiration of the courage shown to rebuild,” at the memorial pool.

At the memorial, they waved briefly to bystanders before heading inside to tour the museum exhibits of artifacts and photographs from the day of the attacks.

Mayor Bill de Blasio later joined Prince William at the Empire State Building for a reception hosted by Shutterstock that celebrated the British talent involved in New York’s growing tech scene. The two checked out some cool gadgets and products created by city startups, like a prosthetic arm, and received an artwork depicting a futuristic New York and Manhattan.

“Let’s give it to [private secretary] Miguel so I can keep it," the Duke said.

The mayor thanked Kate and William for their interest in the city, especially for the duchess paying a visit to needy kids in Harlem Monday.

“I want to just say to His Royal Highness that it means so much to us that you are here in New York City,” de Blasio said.

The royals capped their three day trip in the evening with a gala at the Metropolitan Museum of Art that celebrated the 600th anniversary of their alma mater, the University of St. Andrews.

The mayor said Kate and William are always welcome in the Big Apple.

“I hope this will be the first of many visits — we have many other amenities you have not yet seen,” he said. “We would be very proud to show them to you and it’s a great honor to have you with us.”

The Dutchess brought some holiday cheer to a group of Harlem kids during her first royal outing in the Big Apple on Monday, with the help of the city’s first lady.

Before she and her husband mingled with the Clintons and took in a Nets game at Barclays Center, she paid a morning visit to the Northside Center for Child Development at Madison Avenue and East 110th Street.

Crowds of fans lined up nearby, braving freezing temperatures, and East Harlem residents took in the scene from their windows in a bid to get a glimpse of royalty.

“A princess is coming here! That’s something big and great that never happens,” said Magali Martinez, 49, who has lived on the block for 25 years.

Chirlane McCray arrived first and about 10 minutes later Middleton showed up to a roar of “Kate! Kate! Kate!” from the crowd. The two made their way inside the center, and walked past the awe-struck staff.

“This is a typical day at Northside,” the facility’s executive director Dr. Thelma Dye joked.

The duchess helped the staff wrap presents for the kids in the gymnasium and at one point marveled at the skills of 71-year-old volunteer Mary Dawkins.

“Super speedy,” she said.

Middleton and McCray then met with 3 and 4-year old students with special needs and chatted with them for a while. Two of the students showed their appreciation by presenting the duchess and the first lady with bouquets of roses as they left Northside.

“They thought she was the princess from ‘Frozen,’” administrator Rose Ann Harris said.

Prince William traveled to Washington D.C., meeting President Barack Obama and attending a conference on illegal wildlife trade. The Duke then returned to New York, where he and the Dutchess met Hillary and Chelsea Clinton at the British Consul General’s residence for a reception.

A group of people numbering in the hundreds protested the grand jury decisions in the Michael Brown and Eric Garner cases at Barclays on Monday night. The royals’ security earlier in the day said they expected no major problems.

(with Reuters/Alison Fox/pool report)?