The new President and First Lady Jill Biden wore masks and hugged on a balcony outside their new digs, watching fireworks over the Washington Monument as Katy sang her hit, "Firework."
The "Celebrating America" inauguration concert saved the best for last ... with Katy bringing down the house.
Tom Hanks hosted the 90-minute primetime concert live from D.C., braving a cold winter's night at the Lincoln Memorial.
Former Presidents Bill Clinton, George W. Bush and Barack Obama delivered a special message too ... sending Biden words of encouragement and wishing him success for the good of the country, while taking some subtle shots at the guy Biden's replacing.
Demi Lovato, Justin Timberlake, Bruce Springsteen, Jon Bon Jovi, Foo Fighters and John Legend performed virtually before Katy's grand finale ... as did Ant Clemons, Tim McGraw and Florida Georgia Line's Tyler Hubbard.
After a long day of politics and procedures, Biden's first day in office ended with a bang!!