Queen Elizabeth and Prince Philip Pose for Portrait in Quarantine to Mark Philip's 99th Birthday

Queen Elizabeth and Prince Philip
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The royal couple are currently quarantined at Windsor Castle amid the ongoing coronavirus pandemic.

Happy Birthday, Prince Philip! The Duke of Edinburgh turns 99 on Wednesday and to celebrate the occasion, the retired royal posed with his wife, Queen Elizabeth II, for an official portrait. 

The 94-year-old queen is wearing a floral Angela Kelly dress with the Cullinan V diamond brooch. As for the man of the hour, the Duke of Edinburgh is sporting a Household Division tie. 

The portrait was taken on June 1 at Windsor Castle where the reigning monarch and her husband are currently residing amid quarantine from the coronavirus. 

Philip retired from his public duties in 2017 and royal expert Katie Nicholl says he has no intention of returning to work.

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"I think it's a very unlikely thing that we see Prince Philip in the public eye. ...I think it's very unlikely that we will see him in public," she told ET. "He's in good health but he is obviously incredibly vulnerable and he is in self-isolation with the queen, which I'm told they're surrounded by a very small team of staff. Just a handful of staff between the two of them, which must be quite enjoyable for them not to have the formality of so many courtiers which is what the queen is used to when she's at Buckingham Palace."

On Wednesday, Philip's grandson, Prince William, and his wife, Kate Middleton, wished him a happy birthday on Instagram. "Wishing a very happy 99th Birthday to The Duke of Edinburgh!" read the caption.

Amid the pandemic, Elizabeth and Philip's 71-year-old son, Prince Charles, contracted COVID-19, but only experienced minor symptoms and has since recovered. The incident prompted his two sons, Prince William and Prince Harry, to reconnect after months of tension surrounding Harry and his wife, Meghan Markle's, decision to step down as senior royals. 

"I think with Prince Charles not being well, that really forced the brothers to pick up the phone and get back in touch," Nicholl told ET

For more from the royals, watch the clip below: