FOR THE RECORD: An earlier version of this post misspelled the first name of the wife of Prince Charles as Camila.
After being greeted by the queen and Prince Philip, the president and first lady were shown the six-room suite where they will spend the night. The queen's staff said it was last used by Prince William and the Duchess of Cambridge on their wedding night.
"It may not be the same bed," a palace aide said.
The first couple met for about 10 minutes with the royal newlyweds before participating in a formal welcoming ceremony that included the royal salute by the Guard of Honor.
The queen then hosted a lunch for the president and first lady, which also included Prince Charles and his wife, Camilla, but not Prince William and his wife.
After lunch, the queen led the Obamas on a tour of the royal collection in Buckingham Palace. The president lingered over a page from the personal journal of George III, dating sometime around 1783.
"America is lost!" the king wrote, then going on to muse about the possibilities of trade with the Americans and the importance of "a future friendship and connection."
There was also a copy of "Uncle Tom's Cabin" given to Queen Victoria in 1852, along with the two copies she gave to Prince Albert in 1853. The four also looked at a photograph of the HMS Resolute, timbers from which were used to make the president's desk in the Oval Office.
"We got a pretty good deal out of that," the president said.
Following the palace tour, the Obamas left for Westminster Abbey, where the president was to participate in a wreath-laying ceremony. Obama will then visit with Prime Minister David Cameron at 10 Downing St., and Labor Party leader Edward Miliband, before returning to Buckingham Palace for a state dinner hosted by the queen.