The Black Swan star and her dancer husband, Benjamin Millepied, recently attended a ballet benefit at the royal venue, where she accidentally started a dinner table blaze.
She says, "We drive up and it's all the lords and ladies, it's all, like, the fancy people in England, and we walk in and they have this beautiful performance for us... Prince Charles speaks... and then afterwards they have this long dinner for, like, 200 people at this very long table and they separate the couples.
"My husband is seated at, like, one end and I'm at the other; Prince Charles is like diagonal of me and I'm seated next to all these lords and ladies."
Portman was distracted by the man she was sitting next to and chatting with and did not notice she had placed her programme down on top of a candle on the table.
She continues, "The guy next to me is super nice... and I'm talking to him... and all of sudden he looks over my shoulder and he's like, 'Ahhh,' and I look back... and the table was on fire, and so all these lords and ladies are like smacking it, pouring water, there's, like, 10 guards that rush in..."