The 23-year-old actor has been dating his Twilight co-star for around 12 months. They have both been extremely tight-lipped about their romance, with Robert only confirming Kristen was his "girlfriend" earlier this year.
There have been repeated rumours the young lovers were planning to tie the knot, and Kristen, 20, has now confirmed that Robert did get down on one knee recently - but she assumed he was joking and laughed it off.
"He asked me to marry him," she revealed. "As a joke, though. Well, at least I think so."
Although she wasn`t sure if Robert`s proposal was genuine, Kristen is sure her feelings for him are real. She loves everything about him, from his fondness for speaking in a baby voice to his beautiful singing voice.
"I love Rob because he always wants to be the best," she explained to British newspaper The News of the World. "I love the way he sings, it breaks my heart. And don`t you think he`s just gorgeous? Rob`s also a very bad liar, he just can`t do it!
"But he can be very childish. When Rob does something right or wins something he talks with a different, little voice - like a five-year-old - and every time he looks into a mirror he sees something wrong with his hair."