Teigen, 32, shared the news on Twitter on Thursday May 17 writing, "“Somebody’s herrrrrrre!” along with baby bottle emojis.
Legend then re-tweeted his wife's announcement, but they did not shared any further details about their new family member.
The Sports Illustrated model announced she was pregnant with the couple's second child last November.
"It's John's!" she hilariously captioned a video of her baby bump.
Their little boy joins daughter Luna, 2.