Mendes, who kept a straight face at this point, told DeGeneres, "So ask Gosling about the onesie. Okay, note to self. Ask Gosling about the onesie."
But it was the TV personality's next question that brought out the actress's flushed side.
"So you just call him by the last name?" DeGeneres asked. "You don't call him Ryan? You just call him Gosling – when you see him ever?"
Blushing, Mendes put her head in her hands and covered her face with hair as a set assistant brought out a pink onesie for Mendes and a purple one with duckies for Gosling.
"Because he likes them so much, when you see him – if you see him if you run into him – I've got a gift that I think both of you would have fun [with]," DeGeneres joked once again. "[This could] especially [work] as an icebreaker when you meet him for the first time."