During a lavish banquet at Buckingham Palace on Monday, President Donald Trump noted the coming 75th anniversary of D-Day and the British royal family's steadfastness and dedication during World War II.

At one point, he said: "In April 1945, newspapers featured a picture of the Queen Mother visiting the women's branch of the Army, watching a young woman repair a military truck engine. That young mechanic was the future queen — that great, great woman."

Here's the story behind the photo.

At the outbreak of World War II in 1939, many close to the royal family wanted the Queen Mother and her daughters, princesses Elizabeth and Margaret, then 13 and 9 years old respectively, to evacuate to Canada. But the Queen Mother refused. She rode out the war in Buckingham Palace, though it was bombed repeatedly, and shuffled the princesses around several palaces before settling them into Windsor Castle.

By February 1945, the war was still raging, and Elizabeth had turned 18. At her own insistence, according to the Royal Collection Trust, she joined the Auxiliary Territorial Service as a subaltern and trained as a truck mechanic and driver.

And yes, as Trump said, the Queen Mother visited her daughter in the field, along with Elizabeth's father, King George VI.

By the end of the war later that year, Elizabeth had reached the rank of junior commander. To this day, she is the only female member of the royal family to have served in the military. (You hear that, Princess Charlotte?)

She is also the last remaining head of state to have served during World War II, according to the BBC.

And if you're thinking, "Wait, I don't remember this on 'The Crown,' " well, that's because the Netflix show begins with the engagement of Elizabeth and Philip Mountbatten, which happened after the war. They married in 1947.

But in the very first episode, there's a blink-and-you'll-miss-it reference. While on a trip to Kenya, Elizabeth and Philip's entourage struggles with a stalling car engine. Annoyed, the princess, played by Claire Foy, hops out of the car and tells them how to fix it.

"It's all right, I was a mechanic during the war," she says.