Woman Finds Out Her Favorite Teacher Is Actually Her Biological Older Sister Adopted sisters in upstate New York are reunited after decades of separation.

 -- Thirty years after taking her class, a woman in upstate New York has learned that her favorite teacher is also her biological sister.

Before Diane DiProspero Cook knew that Karen Cometa-Zempel was her older sister, she just thought of her as her favorite teacher at Bryant and Stratton College.

"I used to cry that I wanted a sibling so bad," DiProspero Cook told ABC News.

Both women were adopted into loving homes as infants. The two grew up 20 miles apart in upstate New York, but did not meet until DiProspero Cook walked into Cometa-Zempel's classroom in 1985. They only learned they were sisters last month.

“We lived parallel lives,” DiProspero Cook told ABC News today. "We think alike, we have the same mannerisms."

Cometa-Zempel added, "We finish each other's sentences."

The pair found out they were sisters after receiving a letter from the New York State Adoption Registry with each other's names. They had each reached out independently to the registry to find out a little more about their medical histories, they told ABC News.

Cometa-Zempel said that once she found out the name of her sister, she looked her up on Facebook and noticed they had a mutual friend, who connected the two women. When DiProspero Cook saw the name she thought to herself, "I know her!" As it turned out, Cometa-Zempel taught DiProspero Cook at college back in 1985.

On Valentine's Day weekend, both women were out of town and decided it would be easier to meet up when they both returned to the Spencerport, New York, area. DiProspero Cook said that despite this, they both ran into each other at an outlet mall near Niagara Falls, completely unplanned.

DiProspero Cook said that she could “write a book” of the uncanny things she has in common with her sister. The pair are both left-handed, both attended Catholic school, and both served as care-takers for aging relatives in their families.

The sisters have been working hard at making up for the lost time. Cometa-Zempel said, "The more we talk, the more we find we have in common."