Sally Bedell Smith is convinced Queen Elizabeth won't "retreat from public view".
The 94-year-old monarch is determined to continue with her duties following the death of Prince Philip, according to one royal expert.
Sally Bedell Smith told E! News: "We've become accustomed, since 2017, to seeing her on her own or with other children and grandchildren.
"And so, without him at her side, it's not that unusual. But that doesn't take anything away from the fact that this is going to be a big blow for her. She's been with him for 73 years, and ... as she said, [he's been] her 'strength and her stay' for 73 years."
Sally explained that unlike Queen Victoria - who retreated from public view after the death of her husband, Prince Albert - the monarch doesn't have any intention of taking a step back from her royal duties.
She said: "We're going to see her moving along, doing her duty. She's not going to be like Queen Victoria, and retreat from public view. She'll be out, and she'll do whatever is required of her."
Despite this, Sally acknowledged that Prince Philip - who passed away at the age of 99 - was like "glue" for the royal family and that he'll be a "real loss" for the Queen.
She explained: "She is the queen. And from the very beginning, she made him the head of the family, and he made a lot of the decisions about what various members of the family did. And they would go to him for advice and guidance. I think that will be a real loss.
"They relied on him, he was sort of glue for the family."