Page Six of the New York Post reports that Bilson and Christensen are now engaged.
A source revealed to the paper that the 27-year-old actress was wearing a diamond engagement ring at JFK International Airport on Monday (February 16).
"A man sitting in front of her on the plane saw a ring on her finger and asked if she was married," added the source.
The beautiful brunette replied, "I’m not married yet, just engaged. I know I look like I’m 15 but I’m actually 27."
Bilson and Christensen have been dating for a year, after meeting on the set of the film Jumper.