Cynthia Nixon revealed to “Sex and the City” co-star Kristin Davis on Monday that when she joined the HBO comedy as Miranda, she thought another famous “Kristin” had been cast as Charlotte: “I didn’t know who you were,” she said.

The other Kristin in question? British actress and recently a Best Actress Oscar nominee for “The English Patient,” Kristin Scott Thomas.

Nixon, who played Miranda on the hit HBO series, stopped by Davis’ “Are You a Charlotte?” podcast on Monday and talked about the funny case of mistaken identity as well as their experience on the initial episodes working together.

“Sarah [Jessica Parker] and I knew each other quite well. We’d worked together a bunch of times, and we were always auditioning for the same parts and stuff when we were kids,” Nixon said. “And Kim [Cattrall], I knew a little bit, I’d seen her in a few things.”

“I...