The premiere took place in London in 1999 when Portman was 18 and King Charles was then the Prince of Wales.
Portman, 42, was asked to detail her meeting with the royal while appearing as a guest on Watch What Happens Live with Andy Cohen on Bravo.
When asked by Cohen if she remembered the encounter, Portman said: “A little bit. I remember Prince Charles asked me, he was then Prince Charles, if I was in the originals.”
“I was like, ‘I’m 18.’ But he was very friendly.”
The original Star Wars trilogy was released from 1977 to 1983. Portman was born in 1981.
Portman played Padmé Amidala – Queen and then-senator of Naboo.
The subject of Star Wars was raised after a viewer asked if she’d been approached to return to her character in any of the recent Star Wars spin-off shows.
She said: “No, there have not been [any approaches to her or her team]. No one has asked me, but I'm open to it.”
It comes following news that King Charles is expected to make his first trip to Australia and New Zealand as monarch next year, according to reports in Australia.
The Sydney Morning Herald reported the Queen would accompany her husband on the trip in October.
A source in the Australian government told the paper the trip had not been formally confirmed by Buckingham Palace, but would coincide with the Commonwealth Heads of Government Meeting (CHOGM) in Samoa.
The summit, which takes place every two years and includes the 56 Commonwealth member nations, is scheduled to start on October 21, 2024.
The late Queen made 16 visits to Australia during her reign, each accompanied by the Duke of Edinburgh.
She first visited as monarch in 1954, having stopped in New Zealand en route, with the final one coming in October 2011.
The royal couple’s final visit to New Zealand marked her Golden Jubilee in 2002.
Buckingham Palace has been approached for comment.