When Lucy and Maria Aylmer tell people they are twins, disbelief is one response.

The 18-year-olds from Gloucester, U.K. are two of the five children born to their Caucasian father and "half-Jamaican" mother, World Wide Features reports. While their other siblings have a blend of features from their parents, Lucy and Maria are opposites : Lucy has fair skin and red hair, while Maria has caramel skin and dark hair.

Lucy, left, studies art and design at Gloucester College. Maria studies law and psychology at Cheltenham College.

"No one ever believes we are twins because I am white and Maria is black," Lucy said, according to World Wide Features. "Even when we dress alike, we still dont even look like sisters, let alone twins. When weve met friends for the first time they never believe we are twins and they have even made us produce our birth certificates to prove that we are actually twins."

Fraternal twins develop from two eggs fertilized by separate sperm cells. The BBC reports that for a biracial couple expecting twins , there is about a 1 in 500 chance those twins will have different skin colors.

The Aylmers are proud of their uniqueness.

"Now we have grown older, even though we still look so different, the bond between us is much stronger," Lucy said. "Now we are proud of the fact that we are each others twin sister. Maria loves telling people at college that she has a white twin - and Im very proud of having a black twin."

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