Obama placed her arm around the monarch.
"Yikes! Sorry guys,'" she joked, recalling the moment while speaking at London's O2 arena on Sunday.
Of course, the 55-year-old was unaware of proper royal conduct.
In Obama's defense, the Daily Mail did mention that she recalled the queen calling the monarch-branded protocol "rubbish" at a later visit at Windsor Castle.
When asked if she would have done things differently, Obama said she has no regrets.
"What is true among world leaders is that there are people who handle protocol, and usually the people they're representing don't want all that protocol."
"So you wonder well who are you doing this for because they don't want it, we don't want it."
"But it's just the way things are. So I don't know that I could have done anything differently because it was a natural human reaction."
The queen, however, did not seem bothered by the friendly American gesture.
In fact, Obama recalled commiserating with Queen Elizabeth about having sore feet during the G-20 reception.
"Forget that she sometimes wore a diamond crown and that I'd flown to London on the presidential jet: we were just two tired ladies oppressed by our shoes."
Obama explained how this led to the impromptu hug.
"I then did what's instinctive to me anytime I feel connected to a new person, which is to express my feelings outwardly. I laid a hand affectionately across her shoulder."
She had some explaining to do.
Rest assured the Queen remained unharmed.
Obama added:
"I daresay that the Queen was okay with it, too, because when I touched her, she only pulled closer, resting a gloved hand lightly on the small of my back."
It turns out she had not violated any protocol. An anonymous spokesperson for Buckingham Palace commented that Her Majesty was totally fine over the love pat and confirmed there are no rules that prohibit touching the Queen.
"It was a mutual and spontaneous display of affection. We don't issue instructions on not touching the queen."
When host Stephen Colbert asked Obama what word of advice she would impart to the British on how to stay calm during a time of turmoil, likely referencing the divide over Brexit, she said that London is unique and that they should treasure their diversity.
"This trepidation, the anxiety, it's everywhere, it's all over the world."
"I was looking out over the city, London, a beautiful city, and the thing I love about it is it is truly representative of true international diversity, in ways that you don't see in cities, most cities particularly, even in the United States, and that is a gift."
Obama held a very captive audience at the O2 arena.
Obama's book tour has so far covered North America and Scandinavia and will continue over to Paris and then to Amsterdam.
