Immediately Twitter users began asking where the president's youngest daughter was.
The hashtag "wheressasha" began trending on Twitter shortly after people noticed she wasn't next to her sister.
Twitter users then began theorizing where Sasha may have been.
Sasha stayed back in DC because she has an exam at school in the morning, a White House official said.
Malia Obama is currently taking a gap year before attending Harvard.
Approximately 18,000 people attended the president's farewell speech, according to White House estimates.