The Ford Galaxy with blacked out windows was discreetly waved through the gates of Buckingham Palace and cruised to a halt at the Queen's private entrance.
Out stepped Prince Harry and Meghan Markle. Harry, I understand, was introducing his American actress girlfriend to the Queen. They were there for tea.
I am told it happened on Thursday last week and inevitably it has set tongues wagging at the prospect of a royal engagement.
Ever since Harry issued his edict about privacy 11 months ago when he felt the media were trampling over his romance, royal aides have been extremely cautious about commenting on his private life.
But he desperately wanted his grandmother to meet divorcee Meghan and it would suggest that the couple are making plans for a future together just 18 months after meeting at the Invictus Games in Florida.
Everything about the teatime meeting was deliberately informal, I am told. In part it was to settle any nerves Meghan might have felt but also to ensure it was not widely publicised within the palace.
After being driven in to the inner courtyard, the couple were said to have been whisked up to the Queen's private sitting room on the first floor overlooking the palace gardens and Constitution Hill, and which is served by a lift.
The Queen had only returned from her long summer break at Balmoral Castle two days earlier.
Prince Philip, who has been spending recent times at Sandringham, was not there.
According to an insider the couple arrived in time for tea at around 5pm. It is the Queen's favourite part of the day and she loves it when her grandchildren are able to join her.
She normally sits for half an hour eating from a selection of sandwiches, fruit or plain scones and cake.
It is served with her own blend of Darjeeling and Assam tea, known as Queen Mary's blend.
I understand the Queen spent almost an hour with her grandson and the Los Angeles-born Meghan, who stars in the US legal drama Suits.
Insiders say that Harry, 33, had spoken to his grandmother during the summer at Balmoral asking to introduce Meghan, who is three years his senior.
She has been a regular visitor to the Prince's Kensington Palace home during the past year.
Although she rarely ventures out on shopping expeditions on nearby Kensington High Street as she did a year ago, she is seen walking around the palace complex by royal staff.
I am told that Prince Charles was "very impressed" when he met the actress-cum-activist earlier this year. The Duchess of Cornwall is said to have told a member of staff that Meghan was "a very nice girl and very pleasant".
This, of course, is exactly what Harry has been saying about the girl with whom he is so clearly besotted. After dalliances with Zimbabwe-born Chelsy Davy and actress Cressida Bonas, friends say Meghan is his first "grown-up" love.
It has certainly not followed the pattern of traditional royal romances. Just last month, Meghan took the highly unusual step of publicly declaring her love for Harry in an interview with the magazine Vanity Fair.
"We're a couple, we're in love," she said candidly. Soon they were being photographed together in Toronto - where her TV show is filmed - and holding hands.
No royal boyfriend or girlfriend has spoken so openly about their relationship. The Duchess of Cambridge did not discuss her eight-year relationship with Prince William until they got officially engaged, and then confined her comments to a short television interview.
No wonder betting on an engagement has ended. "It is not a question of if but when," say friends.
Insiders describe Harry's choice of using a people carrier with blacked out windows as unusual. "The royals usually want to make sure they can be seen," one said.
Last night Buckingham Palace referred callers to Kensington Palace, where a spokesman said: "We have refrained from commenting on all previous stories about Prince Harry introducing Meghan Markle to members of the Royal Family and therefore we have no comment."