While speaking to Us Weekly at the opening of Ferrera's new film X/Y Tamblyn revealed the two go on double dates together "all the time -- to an irritating point. I'm not sure who I'm closer with."
"She was one of three people to speak at my wedding. She's one of my best friends," the Two and Half Men actress added.
"Usually America and I going out first, eating and catching up and talking about extensionalism and philosophy, and where we are in our lives. And that usually lasts about 2 hours," Tamblyn shared. "And then the dudes join up and they have been and then we talk about sports for 10 minutes. And then America and I go back to being in love with each other. They go off and do their own thing."
Tamblyn and Ferrera played best friends Carmen and Tibby in the film adaptation of the Ann Brashares novel alongside Blake Lively who played Bidget and Alexis Bleden who played Lena.
The foursome has reunited twice since the filming of the two movies for Lively's wedding to Ryan Reynolds and Tambler's nuptials to David Cross.
The former Joan of Arcadia star has said Lively was "instrumental" in the choosing of her marigold wedding dress.
"I knew I didn't want a white dress and I always thought of kind of a bright jewel tone," she said.