Speaking to Elle, Selena explained how Biebs had hired an entire cinema at LA's massive Staples Center - just so they could watch a film together.
She said: "If I'll share anything with you, it's that he really is a hopeless romantic.
"I had just mentioned it in the car - all I said is that I really want to see Titanic again, and then..."
The 19-year-old spoke about Biebs, her own childhood and her career in the US magazine interview. She also posed for some rather glam photos.
Selena paid tribute to her mum, who brought her up as a single parent in Texas.
She said: "I can remember about seven times when our car got stuck on the highway because we'd run out of gas money."
And she said that her mum still "saved up to take me to concerts. She took me to museums, aquariums, to teach me about the world, about what's real".
Selena also insisted that Disney had not forced her to take a certain path in her career.
She said: "Disney is a machine, so people automatically assume that you can't work for the channel unless you act and sing and dance and sign up for all that.
"That's absolutely not true. I always did everything the way I wanted to do it."
Selena's interview appears in the July 2012 edition of Elle magazine in the US.
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