"I always knew she was going to be the godmother if I had another baby,' King told ELLE in an interview.
The 35-year-old actress is currently pregnant with her second child with husband Kyle Newman.
The couple, who has been married since 2007, has had a son James Knight Newman, born on October 6, 2013. King announced her second pregnancy back in February.
The following month, she confirmed through Instagram posts that Swift would become her upcoming baby's godmother.
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"We try and choose people who we know would raise our child the way that we would raise our child and her thoughtfulness, her kindness, her authenticity... Is so powerful to me. She's so uninhibited in her giving... It's just beyond."
Recalling the day she asked Swift to take on the significant role, King said she did not have a grand plan.
"We were hanging out on the couch and I was like, 'Hey, would ever want to be a godmother?' And she was like, 'Uh, yes!' And she cried and, you know, all the fun things that best friends do," she said.