So what exactly does the role entail?
While she doesn’t attend royal engagements on the Queen’s behalf, she acts as a body double of sorts during rehearsals for major events. As her majesty has a very packed schedule, she is not always able to attend practice runs, which is when Ms Slack is required.
The two are similar in height and stature, meaning that she can help production work out where the Queen should go and how she will fit into the event.
Ms Slack explained: "It started because I was at the BBC and the producer that was doing the cenotaph came to see me and said that the Queen had sent a message to say that when she stood at the cenotaph, the sun was in her eyes and could we do anything about it."
"I said to him, 'Would you like me to come and stand in the position for you?" because all the stage managers were six-foot men!"
Not only has she ridden in the Queen’s royal carriage where she was permitted to try her hand at the royal wave, she has also attended the rehearsal for the state opening or parliament.
And, like her majesty, she also has to follow protocol—and there’s one rule that she absolutely must follow.
She continued: "I’ve never been allowed to sit on the throne at the House of Lords, I have to lurk above it. It’s a very strict rule."
This article originally appeared on marie claire UK.