A new book says Queen Elizabeth said: "Someone must have greased the brakes," after learning of Princess Diana's car crash.
Diana was killed in August 1997, along with her boyfriend Dodi Fayed, when the car they were travelling in crashed in Paris.
As news of the accident reached the Royal Family - before it was realised Diana had died - Her Majesty reportedly issued the remark.
The claims were made in Ingrid Seward's new book, 'An Intimate Portrait of the Queen in Her Own Words'.
The Royal biographer said the comment hinted at the "extraordinary and complex" relationship between the two women.
She said: "At first it was thought that, though the car crash in the Pont de l'Alma tunnel was serious, Diana had not been killed.
"According to one witness present when the Queen heard the initial news, she mused out loud: 'Someone must have greased the brakes'."
Queen was 'bewildered' by criticisms
Diana's untimely death triggered national mourning, and the Queen faced some initial criticism from the public for not leaving her holiday retreat at Balmoral and returning to London immediately.
There was also consternation over the refusal to fly a flag at half mast from Buckingham Palace.
Ms Seward wrote that the Queen was "bewildered" by these criticisms, as the flag not being flown while she was not in residence was "mere protocol".
She claimed the decision to stay in Scotland was made so the young princes William and Harry were given the chance to "absorb the shock of their mother's death" in private.
Her book also claims the Queen was initially very fond of the young Diana Spencer, writing to a friend that: "She is one of us."
But Ms Seward said that, as the princess became nervous and the Queen's concerns about the increased press attention grew, their relationship turned cold, reports The Telegraph.