The 40-year-old actress is seven months pregnant with the 33-year-old actor's child, according to OK! magazine. The pair have been an on-again, off-again couple since they met on the set of The Place Beyond the Pines in 2011.
"She's been ready for motherhood for a while now," a source reveals. "To be sharing this experience with Ryan is a dream come true for her."
Some insiders believe the new baby may help cement the pair's relationship. One source notes that Gosling "grew up without a dad, so he always said when he had kids, he'd be there no matter what." Others think a promise is not enough for Mendes.
"Ryan doesn't think they need to marry just because they are having a baby, but Eva believes it's important to have their lives fully intertwined," a different source says.
Mendes last appeared in Gosling's directorial debut, Lost River. The actor is involved with an untitled Terrence Malick film for 2015.