Sarah Jessica Parker kept Cynthia Nixon's gubernatorial candidacy a secret for a month

You know your sisterly bond runs deep when you're willing to keep a (rather large) secret for your gal pal. And that's exactly what Sarah Jessica Parker says she did for Cynthia Nixon when she found out her Sex and the City costar planned to run for governor of New York one month before the official announcement.

"She shared with me that she was going to announce about a month before. I was incredibly excited and proud of her. I think she's already been good for the conversation," Parker told a large crowd gathered Friday night for a retrospective on her career at the 2018 Tribeca Film Festival in New York City. "This is what's exciting about primaries, right? People can inspire an incumbent to reconsider policy…or just have a robust conversation. She's formidable. She's incredibly bright. She's really brave. She's excited about this race, and it's challenging. But, she seems enormously energized and I think it's good for us to have a competitor — it's always good. A challenger is good."

Nixon, who starred opposite Parker across six seasons of the HBO comedy series, revealed March 19 that she would run against current New York Governor Andrew Cuomo in the upcoming Democratic primary.

"I didn't [anticipate] that she would seek a gubernatorial seat," Parker admitted earlier during the event, going on to explain that the pair formed a close friendship while working the entertainment industry as child actresses. "She's been an activist her entire life. She's incredibly bright, she loves this city, she's been involved in conversations about policies that have been really important to her for many years: Education, public schools, housing…the larger issues that are part of conversations that affect us here [in the city] and upstate as well."

According to the New York Times, Cuomo currently leads Nixon in the polls by 31 points, with a projected 58 percent as opposed to her 27 percent.

Still, the ladies' Sex and the City castmates have also publicly supported Nixon — some in more direct ways than others — following her decision to run for office.

"I support & respect any former colleague's right to make their own career choices," Kim Cattrall tweeted. Kristin Davis added that she's "so proud" of Nixon, whom she indicated would "be an excellent Governor!"

Earlier during the Tribeca Film Festival, Parker attended the world premiere screening of her latest film, Blue Night, about a singer wandering the streets of New York reconnecting with herself — and a few familiar faces from her past — as she comes to terms with her existence in the wake of a grim medical diagnosis.

"I wasn't thinking of it politically, I wasn't looking at its place [in that aspect]. I certainly saw that [my character] was a person who's singular in her approach and independent, but also having made what some might argue as bad choices. Still, I liked her unique approach, even through her day, her choice to be quiet, to reserve information, to retreat. I respected and understood how hard all of that must be, how much you need comfort and how hard it is to ask for it," Parker previously told EW of the film, which she also produced and sees her returning to the art of singing after initially cutting her teeth as a performer in stage musicals like Annie and Once Upon a Mattress. "To feel superior and inferior simultaneously…these are all emotions that lots of women feel across industries: mothers, girlfriends, friends. To have an opportunity to experience so much of that onscreen in two hours or less is unusual. Maybe that's why the experience was so fulfilling."

A representative for Nixon did not immediately respond to EW's request for comment.

—With reporting by Kristen Harding