They've been parents together for just under six months, and it appears that now, Eva Mendes is preparing to take the next step in her relationship with Ryan Gosling.

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According to OK Magazine, the 41-year-old actress and fashion designer is changing her tune about marriage in general, and is making plans for a future wedding to her 34-year-old beau-and has started by picking out what she wants for an engagement ring.

"Her next project will be her engagement to baby daddy Ryan Gosling and she's informed her fiancé-to-be that 'only 10 carats will do'!" sources told the magazine.

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As for why she is demanding a minimum 10 carat ring? The actress is reportedly influenced by the similarly sized heart-shaped sparkler that singer Lady Gaga was recently given by her new fiancé, actor Taylor Kinney-and she wants something what will be comparable to that.

"She wants a 10 carat princess-cut diamond solitaire-she LOVED Lady Gaga's ring and was openly admiring its design to Ryan, who's taking on board all her wishes," the source added.

And it appears her timing is just right, as Gosling is reportedly so enamored by his girlfriend and their daughter, Esmeralda Amada, that he would do anything she asks him.

"Ryan's so amenable right now and completely in love with her and their little girl, and Eva's totally taking advantage of it," the source said.

The couple will reportedly make a formal announcement about their plans for the future soon enough-with them reportedly making plans to get engaged as early as this coming summer-and a wedding may not be that far behind.

"They'll get formally engaged over the summer and don't want a long engagement," the source said.

Tags: ryan gosling Eva Mendes