As the father of twin boys, I'm always fascinated by stories that underscore the similarities and differences that can occur between twins. Marcia and Millie Biggs are twin sisters, but they're often seen as 'friends' because they are biracial.

Marcia has blue eyes, blonde hair, and pale skin, while her fraternal twin sister Millie has darker skin, brown eyes, and jet black hair. Let me just add that both girls are nothing short of beautiful!

“Sometimes people don’t believe us when we say we are twins," Marcia told "Good Morning America." "They think we're just telling a lie."

Their parents, Michael and Amanda Biggs, say the girls looked identical when they were born, and they didn't notice a difference in the girls' complexions until they were about 10 months old.

Their mother calls the girls her "one-in-a-million miracle."

The girls are featured in the April edition of 'National Geographic' magazine.

"I’m proud of us,” Marcia said, looking at her sister. “It’s not every day you’ll see yourself on a magazine. It looks so bold ... I feel special being on the front cover.”