Beyonce portrayed the blues great in the recent film "Cadillac Records" and sings the song in that movie.
Beyonce will sing to the Obamas at the Neighborhood Ball Tuesday night.
In a statement, Beyonce said: "I am so honored that I will be performing for President Obama and the first lady. To sing `At Last' while they have their first dance is a dream come true. I could not be more honored and excited that they have asked me to be part of this moment in history."
It was revealed on Thursday that Beyonce would be serenading the Obamas at the event. But the song choice was not revealed by the Presidential Inaugural Committee.
"It is our hope that we can keep the song secret until the moment," said spokeswoman Linda Douglass.
But Beyonce decided to spill the beans herself Friday. Maybe it reflects her excitement: A day after Obama's victory, Beyonce giddily offered to do anything the Obamas needed at the inauguration during an interview. Beyonce, along with husband Jay-Z, were Obama supporters and went out to campaign for him during the election.
Beyonce recently had a No. 1 hit with her song "Single Ladies," with its catchy refrain to a former love: "If you like it then you should have put a ring on it."
