Relationships
Frederick, who never met her biological father, regarded actor David Niven as her substitute father. They first met while filming the television film adaptation of The Canterville Ghost (1974). They remained close friends over the years until Niven's death in 1983, which occurred just eight weeks after the birth of her daughter.
As a child, Lynne was very close to her mother Iris and grandmother Cecilia. Her relationship with her mother suffered major damage after she married Peter Sellers in 1977. Five days after the wedding, Iris spoke out against the marriage in an interview with the Daily Mirror:
"Time will tell, but I think Lynne has made a terrible mistake. I hope it will work for her sake. He [Peter Sellers] is a brilliant man, but not the kind of son in law I would have chosen. I wasn't invited to the ceremony, but that isn't surprising. When I heard it was taking place, I said: 'The sooner it happens, the sooner it will be over'. Somehow, in view of Sellers's previous record with the ladies who have gone before, I think this marriage may not last too long."
Feeling hurt and betrayed by this interview, Lynne did not see or speak to her mother again for the duration of her marriage to Sellers. When asked about cutting ties with her daughter, Iris said: "I have my own life to live. Of course I still love her. I've cried for her and I miss her a great deal. Lynne is right when she says we were terribly close and it hurts when I see her using the press to make me look the guilty party in all this."
During the period when Iris was not in communication with Lynne, she continued to publicly blast her daughter's marriage in the press.
"My own marriage ended unhappily when Lynne was two. I tried to compensate for her having no father by devoting all the time I wasn't working to her. Perhaps if I had married again she wouldn't gone on choosing men twice her age as boyfriends – looking for a father figure I suppose. She met Peter Sellers on the rebound from David Frost. I thought 'here we go again' but I didn't want to be the one to put it down without giving it a chance. I know I said things later about marital track record not being very good, but at the time I went along with it wondering how long it would be before I was having to give him the 'Lynne regrets' speech. Now I ask you! What mother can be expected to approve of the marriage of her daughter to such a man? My heart bled for her. To me their marriage is doomed right from the start. I hope and pray they'll prove me wrong. God knows I want Lynne to be happy. But this time I must let her sort it out for herself. She must understand that I am staying clear for her sake even though it hurts me to do so."
After Sellers' death in 1980, Frederick reconciled with her mother. Despite its rekindling, their relationship was never the same again.
In 1972, while in her late teens, Frederick became involved with Curzon House Club casino owner Julian Posner, who like Sellers was 30 years her senior. They had an on-and-off relationship for about three years until 1975, while Frederick's acting career continued to blossom. During their off times, Frederick often discreetly engaged in affairs with her friend and future husband David Frost.
Frederick's relationship with her former stepchildren (Michael Sellers, Sarah Sellers, and Victoria Sellers) was, like Peter's relationship with them, distant and often strained. When Lynne began her relationship with Peter, she made efforts to establish a friendly connection with them. Sarah recalled of Lynne: "she seemed quite nice to begin with. I actually told dad that I thought she was a bit stupid. But she came across as very bubbly, friendly, warm and interested. But once they got married things definitely changed". Michael Sellers wrote of Frederick in his exposé memoir: "my first impression of Lynne didn't do much to alter my views. She was not exactly my idea of sweetness and light. It didn't concern me that she lacked the good looks of dad's past wives and girlfriends, but those innocent eyes, certainly her strongest feature, didn't deceive me". Michael Sellers also bluntly acknowledged his intentional hostility and lack of respect towards Lynne when they first met: "I'm afraid we weren't very kind in our judgement of Lynne. Sarah thought she wasn't too bright. But our views didn't really count for much. Because whatever our opinions, they would be of purely academic interest". Months after Frederick's death in 1994, Victoria said "I feel now that she's in hell – I don't know but that makes me feel better."
One of Frederick's close friends was Mauritian actress Françoise Pascal. The two first met when they co-starred on a 1972 episode of the television anthology series BBC Play of the Month, and they quickly became "firm friends". Pascal recalled that they remained friends for several years before regretfully losing touch after Frederick married Sellers in 1977. In April 2020, a few weeks before the 26th anniversary of Frederick's death, Pascal tweeted a photo of herself and Frederick, with the caption "I think of her very often! Always had that fresh baby face! RIP Lynne! Xxx".
In 2018, Judy Matheson revealed that she had worked with Frederick in the early 1970s. They were slated to appear in a film together that was to be shot in the Netherlands, with John Hamil, Robert Coleby, and Nina Francis. Because Frederick was young and a relative newcomer to filmmaking at the time, Matheson (who was a few years older and had industry experience) was asked to be Lynne's chaperone for the trip (as Lynne's mother was unavailable). They spent about three weeks lodged together in a hotel room before production on the film was prematurely closed due to financial withdrawals. Matheson stated that she enjoyed Frederick's company, and that they managed to have fun together despite the production difficulties. After returning to Great Britain, they corresponded for a while before gradually losing touch with each other.
During production of Four of the Apocalypse (1975), she was rumoured to have had a brief romance with her co-star Fabio Testi (who was having trouble in his relationship with actress Ursula Andress at the time), which was also during a time when Frederick was having trouble in her own relationship with Julian Posner. Naturally, this helped Testi and Frederick with their chemistry in the movie, and they were paired again for the film Cormack of the Mounties (1975). There has been much speculation about such a romance between Testi and Frederick, but it has not been confirmed.
In her 2014 memoir I Said Yes to Everything, Lee Grant claimed that during production of the film Voyage of the Damned (1976) Frederick, then aged 21, engaged in an affair with Sam Wanamaker, who was 35 years Frederick's senior and married to Charlotte Holland at the time. Grant also stated that she witnessed all the men on set, including the film's director Stuart Rosenberg, make salacious passes at Frederick, all of which she rejected.
Julie Andrews stated in her 2019 autobiography Home Work: A Memoir of My Hollywood Years that she suspected her husband Blake Edwards was having an affair with Lynne (who was married to Sellers at the time) during production of Revenge of the Pink Panther (1978). When Andrews confronted Blake about the "flirtations" between him and Frederick, Julie asked him point-blank which he preferred: staying married or continuing this flirtation. After this confrontation, Blake apparently ceased any kind of flirtation with Frederick. She later had a falling-out with Edwards and Andrews after successfully suing them for their involvement with the film Trail of the Pink Panther (1982), claiming that it insulted Sellers' memory.