>>> what a story we leave you tonight. the story of two young women who have lived in the same city, washington, d.c., for 17 years, attending different schools. they never crossed path until one day on the race track . life took a surprising turn, and knowing the rest of the story now, it all makes sense. nbc's ron mott has their story.

>> reporter: robin jeter and jordan dickerson are like many kids their age. different schools, similar interests. both smart, popular, athletic. but they knew their families weren't like most others. robin, a senior, grew up in foster care .

>> going from like foster home to foster home , i only grew up with my one brother. and that's like all i knew.

>> reporter: jordan , a junior, was adopted. something her mom never hid.

>> her telling me that i was adopted really wasn't that big of a deal really. i just wanted to know more about it.

>> reporter: strangely enough, jordan joined the track team . something happened that sent her heart and robin's soaring. this past winter at a track meet of all places, one of the great mysteries about their childhoods was suddenly revealed. their lives have been dramatically different ever since. jordan 's teammate william was watching.

>> i said, "go, jordan , go, jordan , go, jordan , go, jordan !" ran across, she turned around. i was like, yeah -- that's not jordan .

>> reporter: it was robin, a mixup he related to jordan .

>> i was like, "she looked just like you!"

>> reporter: moments later, another student cleared up the confusion.

>> i was like, oh, i know that girl. her name's robin jeter . then jordan just started crying.

>> reporter: jeter , jordan knew, was also her birth name .

>> i started crying in the middle of the track meet, in the middle of the bleachers. i was freaking out. i was hysterical.

>> reporter: at long last, two sisters met.

>> i couldn't even say anything.

>> i was like, hi. the only thing i could say was, you know we look a lot alike.

>> reporter: jordan was aware she had a sister out there somewhere. for robin, it was a complete surprise.

>> who you look like?

>> you. you. you.

>> reporter: her friends have been wondering where she's been lately.

>> i told them i was like, "i'm still going to be here, but i got to catch up on 17 years that i missed out and never known his a sister."

>> reporter: divided by time and a few miles. now inseparable. ron mott, nbc news, washington.