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Shock and tears as Ayanna Pressley learns she won the House primary in Massachusetts

(CNN) Before Ayanna Pressley celebrated her triumph surrounded by dozens of supporters, a wave of shock hit her behind closed doors.

On Tuesday, Pressley became the latest primary challenger to upset a sitting Democratic member of Congress, defeating 10-term incumbent Rep. Mike Capuano in the Boston-area district once represented by John F. Kennedy.

When the 44-year-old rising star in the Democratic Party heard the results, she just couldn't believe it.

"We won? we won?" she repeats as she looks around the room.

In a video posted by her close friend Jesse Mermell, Pressley stands up in seeming disbelief. Moments later, her husband hugs her and she breaks down in tears.

Joy, laughter and more tears continued as the night went on.

Later during Pressley's victory party, her stepdaughter Cora stood in silence with tears rolling down her face as she listened to Pressley speak.

Ayanna Pressley's stepdaughter, Cora Harris, cries during her victory speech onTuesday night.

"It seems like change is on the way," Pressley told the crowd.

"When I was growing up, my mother and I felt voiceless and invisible, but she made sure I knew that on Election Day we were powerful," she said during her speech.

Pressley's win was one for the history books. She is poised to become the only black member of Massachusetts' mostly male congressional delegation. She also would be the first person of color to ever represent the state in Congress.

She is expected to coast to victory in November as there is no Republican on the ballot.

CNN's Eric Bradner contributed to this report.
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