Mendes and Gosling 'have baby girl'
Us Weekly said that the Hollywood stars' first child was born on September 12.
Hitch actress Eva, 40, and Drive actor Ryan, 33, have kept schtum on reports that they are expecting a child together.
They first began dating in 2011 after co-starring as parents in crime drama The Place Beyond The Pines.
In February, Eva denied she was pregnant after she sparked rumours she could be expecting when she would not go through airport scanners.
She told The Ellen DeGeneres Show. "It's so ridiculous. It all started because I didn't want to go through the scanners at the airport. You know those X-ray scanners, which are really creepy? They basically see you naked, right? And not only that, but there's a radiation aspect to it, so I always opt out."
Us Weekly previously quoted a source as saying that Lost River director Ryan "has already stepped into the role of caring father-to-be".