“Someone had said, ‘when you two meet, there is going to be a chemical reaction.’ I had been really excited for this girl to land in Wilmington [North Carolina],” Williams tells PEOPLE.
Williams, 37, says when Philipps, 38, joined the Creek cast the two hit it off instantly.
“She was so beautiful and cool. She wore overalls and her hair was in braids and she was so real, tough and funny,” says Williams. “We became inseparable and I fell in love with her.”
For more on Williams and Philipps pick up this week’s issue of PEOPLE on newsstands Friday.
The best friends are getting a chance to work together again in the upcoming comedy I Feel Pretty. In the film, Philipps plays the friend of a woman (Amy Schumer) who hits her head and wakes up thinking she’s gorgeous. Williams plays Schumer’s boss at a cosmetics company.
Philipps, who is mom to Birdie, 9, and Cricket, 4, says she and Williams have many things in common besides becoming TV stars at a young age.
“We both had our kids around the same time. We are interested in the same kinds of books and poetry and music, wine and beach vacations,” she says.
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For Williams, her BFF is a constant guiding force and has been a source of support throughout her life.
“I said to her recently, ‘you have really saved me from every being lonely because you are always right there'” says Williams. “We are so close and can tell each other everything. I don’t know what I would be or who would be without Busy.”
I Feel Pretty hits theaters April 20.