Claire Foy, Queen Elizabeth in the acclaimed Netflix series The Crown, was paid less than her on-screen Duke of Edinburgh Matt Smith.
Despite Foy's Golden Globe-winning performance, Smith's previous work on Dr Who earned him higher pay, the show's producers said.
They said it would not be the case for the third series, when Olivia Colman replaces Foy.
It is the latest example of the gender pay gap in the industry.
Earlier this year it was disclosed that Michelle Williams was paid a fraction of what her All The Money In The World co-star Mark Wahlberg earned for reshooting sections of the movie.
According to Hollywood trade publication Variety, The Crown's producers said Smith's Dr Who fame meant he commanded a bigger salary.
Foy, 33, who before The Crown appeared in the BBC's Wolf Hall, was reportedly paid $40,000 (£28,000) per episode for the first two series, which portrayed the monarch in the 1950s and 1960s.
It is unclear what Smith was paid.
The Crown co-producer Suzanne Mackie told a television industry conference in Jerusalem that the pay difference would be rectified.
"Going forward, no-one gets paid more than the queen," Variety quoted Ms Mackie as saying.
For the third series, which moves into the 1970s, Prince Philip will also be played by a different actor.
The Crown is one of the most expensive television shows ever produced, costing about $130m (£93m) for the first season alone.
The ongoing disparity between men and women in the entertainment business is reflected in annual lists published by Forbes magazine.
In 2017, Emma Stone topped the best-paid actress list with $26m (£18m), while Mark Wahlberg was the highest paid man with $68m in estimated annual earnings.
When it was revealed that Wahlberg was paid $1.5m (£1m) for his All the Money in the World reshoots – while his co-star Michelle Williams got $1,000 – he donated the money to Time's Up, the campaign against workplace sexual misconduct.