Tabloid reporters have obtained a copy of the birth certificate (seen here), which lists Hugh John Mungo Grant as the father of a baby boy whose surname is also Grant.
The 53-year-old actor already has two children, daughter Tabitha and son Felix, with Tinglan Hong. Eberstein gave birth to the boy three months before Hong gave birth to Felix.
Grant's name was originally left off the birth certificate until it was re-filed in December of last year.
"Everyone was right all these years, saying, 'Hugh, why don't you have some children? It changes your life,'" Grant told Ellen DeGeneres in 2012. "Now that I have a child, it is life changing. I recommend it. Get some!"