Queen Elizabeth II knew that Prince Philip did not have long left to live following a series of health scares, and so she was prepared to say goodbye.

The Duke of Edinburgh died on April 9 after weeks in the hospital because of his frail health. He reportedly died from old age and in his sleep in Windsor Castle, where he spent his remaining days in the company of his wife of more than 70 years.

According to a royal expert, the British monarch knew and saw that her husband was "getting old and weak." She was more than prepared to see him go so he can finally rest.

"The Queen has always been good in a crisis. She doesn't panic, she doesn't collapse. She's a pragmatist," Robert Hardman told OK.

He said Queen Elizabeth II had "been worried" about Prince Philip "for a long time." He added, "but one of the upsides of lockdown is that they were together a lot more than they would have been." Her Majesty relied on the Duke of Edinburgh a lot, "but he was getting old and weak and she knew that" it was time for him to go.

Hardman, author of "Queen of our Times: The Life of Elizabeth II," said the monarch "was prepared, and had the wherewithal to deal with his death."

On March 29, the British royal family will gather for a Thanksgiving service to celebrate the life of Prince Philip at Westminister Abbey. Despite relying on a walking stick and reports of her being in a wheelchair, the 96-year old monarch "still hopes to attend" the ceremony.

As such, senior aides at Buckingham Palace want to ensure she is in good health in the lead-up to the service. They have advised her to pace her engagements so she still has the energy to travel to London.

Queen Elizabeth II has so far only committed to doing in-person engagements at Windsor Castle following her COVID-19 recovery. It is said that for her trip to Westminster Abbey for Prince Philip's memorial, she will take a 15-minute helicopter ride. She will also rely on a wheelchair to get inside the abbey and to her seat.

Queen Elizabeth II and Prince Philip
Prince Philip was married to Queen Elizabeth for seven decades Photo: AFP / Filippo MONTEFORTE