Ms Sturgeon told an audience at the Aye Write book festival in the Royal Concert Hall in Glasgow on Friday evening she did not know who Alister Jack was after he had been appointed by Boris Johnson.
The revelation came as part of an in conversation event with comedian Janey Godley to discuss her new novel.
Ms Sturgeon and Godley discussed one of the now infamous voiceover clips Godley became known for where she pretended to be Nicola Sturgeon when Boris Johnson attempted to usher her into Bute House in 2019 when he became Prime Minister.
Ms Sturgeon said she did not know who Mr Jack was and she first met him on the steps of Bute House.
She said: “I hadn’t met him before. I literally had no idea who he was.
“I just thought: ‘Who are you?’
“That was also the time Boris left by the back door.”
Ms Sturgeon also revealed they had “kind of kidnapped” Mr Jack on his first visit to Bute House in 2019.
She said: “In between him (Boris Johnson) arriving and him leaving, we kind of kidnapped Alister Jack.
“But that’s another story for another time,” she joked.
“I’ll leave that one for the memoir.”
Ms Sturgeon, who is facing questions over her party’s financial management while she was leader and first minister, said the event was the “best therapy” she had had in a long time.
Friday’s event ended with Godley performing a special voiceover which acknowledged the “stress” Ms Sturgeon had been under in recent weeks as a result of the police investigation into the SNP’s finances and the arrest of her husband, ex-SNP chief executive, Peter Murrell.
