Winfrey – who stars with Kaling in the upcoming big screen adaptation of A Wrinkle In Time – tells PEOPLE that she was standing in the film’s press line at Disney’s D23 expo earlier this month when her castmate told her that she’s expecting.
“That’s when she told me. My mouth dropped,” recalls Winfrey. ” ‘What did you just say?’ she said, ‘Oh, Oprah, I don’t think you know. I’m 5 months pregnant.’ And I said, ‘WHAAAAT?!’ ”
Continues the 63-year-old, “That was it, and we just kept smiling. And then I said to [Reese Witherspoon], ‘Did you know?’ and she said, ‘I just found out, too.’ And then I said to [Wrinkle director Ava DuVernay], ‘Did you know?’ And she said, ‘I just found out.’ ”
Winfrey says that “none” of the Wrinkle team knew ahead of that moment, but adds, “I’m excited for her.”
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News of Kaling’s pregnancy broke on July 17, with a source previously telling PEOPLE that she “just started telling her friends that she’s pregnant, but she’s not telling anyone — not even close friends — who the father is.”
RELATED VIDEO: Pregnant Mindy Kaling Debuts Baby Bump — & Says The Mindy Project Will Tackle ‘Mom Shaming’
Though the star has yet to publicly address the baby news, she debuted her baby bump for the first time on Thursday at the Television Critics Association panel for her show, The Mindy Project, at the Beverly Hilton.
Another insider told PEOPLE that friends think Kaling will make an excellent mom, saying, “Mindy is really motherly to the people she loves and…