In the 18 months since he took office, Mayor Bill de Blasio and his predecessor, Michael Bloomberg, have rarely shared the same stage. It took a groundbreaking for a new graduate school seen as crucial for the city's future to bring them together on Tuesday. NY1's Lindsey Christ filed this report.

Former Mayor Michael Bloomberg has steered clear of city matters since leaving office - but he reemerged Tuesday—with Mayor Bill de Blasio, of all people—to break ground on Roosevelt Island for the new Cornell Tech graduate center, a pet project of Bloomberg's as mayor and now a focus of his philanthropy.

"As an engineering major in college, it's exciting to think of the classes that will go on here. For the record, I would not have gotten into Cornell Tech," Bloomberg said.

Bloomberg announced a $100 million dollar gift, a secret to Team de Blasio until Monday. 

"Mayor Bloomberg, I have to tell know how to steal the show!" said Lieutenant Governor Kathy Hochul.

De Blasio often criticizes Bloomberg, but this was a day of mutual praise.

"I want to give Michael Bloomberg a true compliment because he doesn't usually do things halfway. And he believed in this vision in this possibility for New York City," de Blasio said.

Cornell won a competition to build the school on Roosevelt Island training engineers and applied scientists in business, media and health. 

Phase One is to open in 2017 and include an academic building named the Bloomberg Center, in honor of the former mayor's two daughters. 

"This project represents New York City's next chapter. It's a story that will be written by their generation. I've said before there is no greater inheritance I can leave to my daughters than helping to make the world a better place," Bloomberg said.

By 2043, the campus is expected to be completed and serve 2,500 students. Cornell Tech has already been operating for two years, in space donated by Google in Chelsea. 

Both the current and the former mayor spoke about how initiatives like Cornell Tech are helping to transform New York into a hub for technology businesses over the past few years.

It's an effort Mayor Bloomberg focused on and Mayor de Blasio says he's committed to continuing.