In The Crown season 4, Prince Andrew (Tom Byrne) tells his mother, Queen Elizabeth II (Olivia Colman), about an American actress he is dating but neither of them state her name. Here is what actually happened to Prince Andrew's ex, Koo Stark, and what became of their relationship.
Prince Andrew, Duke of York, and Prince Edward, Earl of Wessex, are the two youngest children of Queen Elizabeth II and Prince Philip. They appeared as children in The Crown season 3, which was set between 1964-1977, most notably in the episode "Moonshot" where they watched the Apollo 11 astronauts' 1969 moon landing on television before meeting Neil Armstrong, Buzz Aldrin, and Michael Collins at Buckingham Palace. The Crown season 4 reintroduces the older Prince Andrew and Prince Edward (Angus Imrie) in the fourth episode, "Favourites", wherein the Queen tries to determine which of her four children, including Prince Charles (John O'Connor) and Princess Anne (Erin Doherty), is her favorite.
When the Queen "auditions" Prince Andrew over a poached salmon lunch at Windsor Castle in 1982, the future Duke of York tells his mum about his love life. The prince is 22 years old at this time and he's a member of the Royal Navy about to see action in the Falklands War while serving aboard the HMS Invincible. But Prince Andrew, who at this point is second-in-line to the throne, is also an eligible bachelor and he boasts to the Queen about the American actress he is dating, who was known for appearing in the erotic films Marquis de Sade and The Awakening of Emily, which Prince Andrew describes in sordid detail, perhaps trying to shock his mother. However, that relationship ends off-screen and Prince Andrew marries Sarah Ferguson (Jessica Aquilina) in 1986.
In real-life, Kathleen "Koo" Starrk starred in her infamous erotic films as a teenager, which involved a lesbian shower scene and torturing naked women. But prior to this, Koo had a small role in The Rocky Horror Picture Show, and she played Carnie Marstrap in Star Wars, but her scenes were cut. Stark met Prince Andrew at his 21st birthday party in 1981 and they began a relationship. By accounts, Prince Andrew was in love with Koo and the royal family thought highly of her. The Queen even described her as "elegant, intelligent, and discreet."
Regardless, Stark's racy films came back to haunt her and ensured that she could never become one of the Royals. In October 1982, Prince Andrew vacationed in Mustique with Koo and they were stalked by paparazzi, which publicly revealed their relationship. They found themselves at the center of a media firestorm when they returned to London. Under intense pressure from the public and the palace, Prince Andrew and Koo Stark called it quits, since she could not be accepted as a member of the royal family. However, the Duke of York and Stark remained friends ever since.
In The Crown, Queen Elizabeth laments about Prince Andrew to Prince Philip and says, "If he doesn't change...", which is the Netflix historical series' nod at the numerous controversies that now surround Prince Andrew. Because of allegations of sexual abuse and his connections to the late convicted sex offender, Jeffrey Epstein, the Duke of York had to permanently resign from all of his public roles in May 2020. However, Koo Stark publicly defended Prince Andrew, who is godfather to her daughter, and stated that he was a good man.