Gemma Gibbons feared being sent to the Tower of London for protocol misdemeanour
The judo star tweeted: "Met the queen today, she has very posh toilets! #howtheroyalspee (sic)."
Gibbons said that she was worried about ending up in the Tower of London, as guests at the royal reception for Paralympians and Olympians were instructed not to use mobile phones.
She told MailOnline.co.uk: "I was delighted to have received an invitation to the palace and even managed to exchange a few words with the Queen. I couldn't believe what [the toilets] were like when I saw them.
"There was carpet in them for a start. I have never seen anything so posh. I just took one look at them and thought 'oh, what the hell' and took a picture.
"I tweeted it without thinking, really, and I really hope that I'm not in trouble. It was such a lovely event that I wouldn't want to end up in the Tower."
However, a palace official insisted there was no problem and were glad the Olympians had enjoyed their visit - "wherever they might be in the palace".
The Queen and her husband Prince Philip had welcomed senior figures including Prime Minister David Cameron to the Palace's 18th Century Room before the arrival of the athletes, who were quick to express their delight at the glittering reception.
Double bronze medallist Rebecca Adlington later wrote: "Had an amazing time tonight at Buckingham Palace with all the medallists from the Olympics + Paralympics! So nice to see everyone again (sic)!"