The pair dated amid the actress' relationship with Max Minghella.
"The first person I fell for after my heart was broken was Kate Mara," Page writes. "She had a boyfriend at the time, the lovely and talented Max Minghella."
The romance started in 2014, shortly after Page publicly came out as gay. According to the actor, Minghella was supportive of Mara exploring her feelings for Page.
"I never thought I could be in love with two people and now I know I can," Page says Mara told him. "This was right after I'd come out as gay and it was a time of exploration and also heartbreak."
"I think my relationship, or whatever you want to call it with Kate, very much encapsulates a certain dynamic that I consistently found myself in, which was falling for people that -- I think a lot of us do this -- who aren't fully available," he adds. "And the sort of safety in that and the highs and the lows and the serotonin bump, and then it goes away. And I think that is definitely a pattern in my life."
Mara and Minghella ended up calling it quits in 2014. She married Jamie Bell in 2017. As for Page and Mara, the actor says he's still close to his ex, who has already read his forthcoming memoir.
"I think the love and care that we have for each other is its very own special thing," he says. "Separate from the intimacy that I write about."
Page's relationship with Mara isn't the only past romance he discusses. In his book, Page recalls a secret romance he had with an unnamed closeted female co-star.
The two-year-long romance consisted of Page and his unnamed love secretly holding hands on set, but pretending to be friends elsewhere in public. Page tells the outlet that they were trailed by paparazzi, would leave hotels from different doors and not look at each other in public.
"Some of my friends didn't even know I was in a relationship," Page says. "Ultimately, I do think she loved me. We loved each other and that was very real in our bubble. It was fantastic. You know, it was really beautiful. I admired her and how she inspired me in many ways. But feeling hidden was far too painful. That was impossible and not a sustainable relationship at all. And it taught me that I was not gonna do that again."
Romantic relationships aren't the sole focus of Pageboy. In another excerpt obtained by the outlet, Page describes an encounter with an A-list star at a 2014 birthday party.
"You aren't gay. That doesn’t exist. You are just afraid of men. I'm going to f**k you to make you realize you aren't gay." Page says the star told him.
"I've had some version of that happen many times throughout my life. A lot of queer and trans people deal with it incessantly," Page tells the outlet. "These moments that we often like don't talk about or we're supposed to just brush off, when actually it's very awful."
"I put that story in the book because it’s about highlighting the reality, the s**t we deal with and what gets sent to us constantly, particularly in environments that are predominantly cis and heterosexual," he continues. "How we navigate that world where you either have more extreme, overt moments like that. Or you have the more, like, subtle jokes. [In Hollywood] these are very powerful people. They're the ones choosing what stories are being told and creating content for people to see all around the world."
As for the identity of the A-lister, Page says he's "purposely not sharing his name," but did note, "He will hear about this and know it's him."
Today, Page, who came out as transgender in 2020, is grateful to "feel a way that I never thought I would get to feel."
"I think that mostly manifests in how present I feel. The sort of ease and the ability to exist. There's been periods in my life where I really felt like I wasn't," he says. "We talk about trans joy and euphoria and all of those things and so much of it is in the stillness. I just feel so lucky."
Page announced Pageboy, which will cover his relationship with his body and his experiences as one of the most famous trans people in the world, in December 2022.
"Trans people are facing increasing attacks, from physical violence to the banning of healthcare, and our humanity is regularly 'debated' in the media," he wrote on Instagram at the time. "The act of writing, reading, and sharing the multitude of our experiences is an important step in standing up to those who wish to silence and harm us. Books have helped me, saved me even, so I hope this can help someone feel less alone, feel seen, no matter who they are or what path they are on."
Pageboy will hit shelves June 6.