Princess Eugenie and her husband, Jack Brooksbank, were told to "prepare for the worst" after his father contracted coronavirus.
George Brooksbank, 71, fell ill in March following a trip to France and spent five weeks on a ventilator at London's Chelsea and Westminster hospital, before undergoing a tracheotomy - a procedure to assist with breathing - and being transferred to a ward specialising in heart and lung conditions in those with Covid-19 at the Royal Brompton Hospital and later a further rehabilitation period at a facility in Surrey, and he is thankfully now "absolutely fine" after a total of nine weeks of treatment.
Eugenie's mother-in-law, Jack's wife Nicola - who also contracted the disease but didn't need hospital treatment - praised the NHS for saving her husband.
She said: "Without doubt, they saved him, and we could not be more grateful. We were not able to see him throughout his treatment and more than once we were told to expect the worst."
George has praised the "incredible" treatment he received in hospital and offered his "profound thanks" to all the staff who cared for him.
He said: "I'm walking around at the moment on one stick and I hope to get free of that next week. My breathing is back to normal and I count myself extremely lucky. My thoughts now are with those still battling this disease and the NHS staff risking their own lives to help them.
"The point I really want to get across is that I think the NHS is absolutely magnificent.
"The way I was treated was incredible. Nothing was too much trouble and at no point did I get a sense of a shortage of doctors or nurses or any impression that the service was in any way overwhelmed.
"There was always somebody at hand. I want to offer profound thanks to everyone who was involved. It was a real eye-opener for somebody who has not been in hospital before for any length of time. I certainly owe them my life."