"She won't dwell on the exit," royal biographer Ingrid Seward tells PEOPLE

Although she publicly said she is “entirely supportive” of Prince Harry and Meghan Markle’s decision to leave royal life, privately the Queen – who puts duty before everything — would find such a choice unimaginable in her own life.

“The Queen will be very disappointed,” royal historian Robert Lacey tells PEOPLE. “Her job is to survive” — and to ensure that the monarch survives.

But this isn’t the first time she has encountered an unhappy royal spare – and it was her experience with her younger sister Princess Margaret that influenced her decision to let Harry set out on his own.

“She has a particular sensitivity to what Harry has been going through because of her closeness to Margaret and seeing the same dramas and tensions played out two generations ago,” says Lacey.

Queen Elizabeth II speaks with Prince Harry, Duke of Sussex
Queen Elizabeth and Prince Harry
| Credit: Steve Parsons - WPA Pool/Getty
Princess Margaret, Prince Harry
Credit: Hulton Archive/Getty Images; EAMONN M. MCCORMACK/Getty Images

Margaret struggled with her place in the shadow of her older sister.

“The younger-sibling syndrome is an enduring problem,” says Lacey. “The system has not found a way of giving them the recognition that they need.”

And as the older sibling has children, the problem only gets worse.

“Until Elizabeth produced heirs, Margaret was a possible future Queen,” adds Lacey. “It is a family situation of conflict that goes back over generations.”

Queen Elizabeth
Princess Margaret and Queen Elizabeth in 1942
| Credit: Studio Lisa/Getty

The new arrangements for Harry and Meghan will be reviewed in a year.

“She won’t dwell on the exit,” royal biographer Ingrid Seward says. “She is very pragmatic. She has left the door open for Harry especially — the year of review was with Harry in mind.”

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Sussex Royals
Meghan Markle, Prince Harry and Queen Elizabeth
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Meghan and Harry will reunite with the Queen and the rest of the royal family for the annual Commonwealth service at Westminster Abbey on March 9. The pair will also attend Endeavour Fund Awards on March 5, which acknowledges the wounded, injured and sick service personnel and veterans who used sports as part of their journey to recovery, and they will be at the Mountbatten Music Festival at the Royal Albert Hall on March 7.

Following their outings, the couple will return to Canada where they are beginning to settle into their new non-royal life with their son Archie.