Shortly after taking the stage tonight for a fundraiser at the historic Apollo Theater in Harlem, President Obama broke into song.

Obama, standing behind the presidential podium, thanked his hosts and the performers who preceded him, including soul singer Al Green.

"To know that Rev. Al Green was here!" Obama said.

Then, after a pause, he began to sing the opening line of one of Green's hit songs from 1972: "Let's Stay Together."

"I'm…. sooo in love…."

The crowd of 1,400 supporters went wild.

The lyrics of full opening stanza of the song read: "I'm, I'm so in love with you. Whatever you want to do. Is alright with me 'Cause you make me feel, so brand new. And I want to spend my life with you."

The tune's refrain underscores a theme of Obama's re-election campaign: "Let's, let's stay together. Loving you whether, whether. Times are good or bad, happy or sad." (The president did not sing this part, however.)

"Those guys didn't think I would do it. I told you I was going to do it," Obama said with a smile and a chuckle, looking off stage.

"The sandman did not come out. Now don't worry, (inaudible) I cannot sing like you, but I just wanted to show my appreciation," he said.

The Apollo event was Obama's fourth campaign event of the night in New York City. It was hosted by Tony Award-winning composer and actor Lin-Manuel Miranda with performances by soul singer Green and vocal artist India.Arie. Tickets were $200 apiece for general admission.