US President Barack Obama and First Lady Michelle Obama attend the Inaugural Ball at the Walter E. Washington Convention Center on January 21, 2013 in Washington, DC. Credit: MANDEL NGAN/AFP/Getty Images

There's no house party like a White House party! On the evening of Monday Jan. 21 -- following more public, official inauguration galas -- President Barack Obama and First Lady Michelle Obama opened up their historic Washington, D.C. home to about 400 super-VIP guests for a private shindig.

A source tells Us Weekly that the party began around 9 p.m., with a staggering array of boldfaced names from politics, music and movies arriving for cocktails, a late buffet and dancing: Washington heavyweights Bill Clinton, Colin Powell, Madeline Albright, John Kerry, Eric Holder plus Alicia Keys and husband Swizz Beatz, Usher, John Legend and fiancee Chrissy Teigen, Katy Perry and  John Mayer, Kelly Clarkson and fiance Brandon Blackstock, Jennifer Hudson, Kerry Washington, Eva Longoria, Brad Paisley, Ashley Judd and Gayle King, to name just a few.

Mr. and Mrs. Obama arrived for the festivities around 10 p.m. alongside daughters Malia, 14, and Sasha, 11. Once it was time for DJ Cassidy to spin some tunes, the floor was cleared for dancing -- and live performances from the likes of Eric Benet, Janelle Monae and Ledisi. During Cassidy's DJ set, Usher, Perry, Keys and Hudson each took the floor to sing along to their hits.

"The party went on until 2 a.m.!" the source marvels to Us, adding that the President and his family all hit the dance floor. "They all stayed until the end… Obama was dancing with everyone and let his guard down!"

"Teenage Dream" singer Perry, 28, tweeted about the unforgettable bash. "Just left the White House. All other parties from here on out will be judged unless they take place at the White House."

"Just partied at the White House," added Clarkson, who sang "My Country Tis of Thee" during the inauguration ceremony earlier in the day. "I kid you not, Michelle Obama stood up and got the party started ....seriously cool First Lady."