"I was keeping my pregnancy pretty low key but unfortunately my mother has Instagram. Which, mothers and Instagram, it's a bad combination," Roberts quipped. "She definitely spilled the beans."
Noting that her mom didn't have a computer and had a flip phone until recently, Roberts shared that a few years ago, she bought her mom an iPhone.
"It was the worst thing I ever did," she admitted, laughing. "It started slow with a Google Alert on me, which she never had before, so she's like, 'Emma, have you seen this photo from 2010?!' I'm like, 'Yes, I've seen that photo.' So I'm getting flooded with 'Is this true?' And 'Have you seen this and that?' And then she got Instagram."
Roberts noted that her mom wasn't tech savvy and got "totally catfished" by someone claiming to be singer Jackson Browne.
"It led to interacting with my fans and just thanking them for all their pregnancy wishes," Roberts said. "It was a disaster, and I found it all out on a plane, so I couldn't get to her. I couldn't call her or attack her."
Cunningham responded to many fans offering her daughter well wishes on her pregnancy after a tabloid reported that Roberts and her boyfriend, Garrett Hedlund, were expecting their first child together.
"She was like, 'Thank you so much for the well-wishes! We're so excited.' It was endless. My friends were sending me screen grabs," the American Horror Story actress recalled. "It was unbelievable. When I said to her, 'Mom, you revealed my pregnancy.' She goes, 'Emma, you announced it!' And I said, 'No I didn't. That was a tabloid.' She goes, 'Oh I didn't... that wasn't clear.'"
As for the aftermath, Roberts tried to teach her mom a lesson.
"We kind of laughed. We kind of got into a fight. I blocked her at one point," she quipped, adding that it's a "good story to tell the baby."
Roberts also opened up about trying to pick out names for her baby boy with Hedlund.
"I was convinced I was having a girl to a point where I said to my boyfriend, 'If it's boy you can name it,'" she said, laughing. "Meanwhile being like, it's a girl, who cares? Now I get to name it. Then when we found out, he was like, 'Oh yeah, so you said I get to name it!' And I was like, 'I did say that, didn't I? So funny that I said that.'"
The Dirt Music actor, 36, eventually picked the name for the couple's baby boy.
"My boyfriend was playing very hard to get with me about the names. I was like, 'We're having a baby. You can tell me what you want to name the baby,'" Roberts said of Hedlund. "And he was just very tight-lipped and then he did finally, he came up with a winner that was really good. All of mine got vetoed for various reasons, which I'm very upset about."
Roberts is currently starring in the Netflix rom com, Holidate, and when asked about her personal favorite romcom, she kept her answer close to home. Roberts named the 1997 classic, My Best Friend's Wedding, starring her A-list aunt, Julia Roberts.
"It's comforting to me! That movie makes me laugh so hard and yes my aunt happens to be in it, and be amazing, but it's like the one movie that's on my computer and I watch whenever I'm homesick," she shared. "It's probably partially because of her but partially because it's such a great movie."