Newlyweds Ashlee Simpson and Evan Ross have filed legal paperwork to change their last names.

Jessica Simpson's younger sister wed the son of superstar Diana Ross in August (14), and took on her new husband's legal last name of Naess.

However, the couple is now seeking to amend its surname to Ross-Naess, according to

The motion will be addressed in court at the end of January (15), when a judge will decide on whether to sign off on the request.

It is unclear why Simpson and Ross, who are reportedly expecting their first child together, want to change their surnames.

Ross is the son of singer Diana and her second husband Arne Naess, Jr.