On Sept. 14, 1982, Grace Kelly died at the age of just 52 after a tragic car accident.

Prince Albert was only in his early 20s when he lost his mother. In an interview with In Depth, the royal spoke more openly than ever about the moment he found out about her death.

Prince Albert on the tragic death of Grace Kelly

The day before she died, Princess Grace was on her way to the palace with her then 17-year-old daughter Stéphanie.

They were coming from the summer residence of the Princely House when the car veered off the road and went down a slope. Prince Albert learned of the accident from his father, Prince Rainier.

"Basically he said that we had to go down the hospital because mom and Stephanie had an accident," Albert recalled.

"I didn't think twice about it and went down with him, [my sister, Princess Caroline] as well, and of course it was a very shocking moment." His sister and mother were rushed to hospital with serious injuries after the accident. Anxious moments followed.

The tragic life of Grace Kelly

Albert continued in the interview: "You're not sure what to think. Of course you think that things are going to improve and it's not as bad an accident as you thought it was...

"It wasn't until later that evening that it became apparent that the outcome was not going to be a good one," he explained.

Grace Kelly died a day after the serious crash. It's long been speculated that the Rear Window actress lost control of her car due to a stroke.

The fact that her mother died and Stéphanie survived was something Albert's sister struggled with, the Prince also revealed: "It was a very painful recollection for her, and it took a number of years for her to come to terms with that."

His father, Prince Rainier, also struggled all his life with the loss of his great love, Prince Albert said. Until his death in 2005, Rainier never remarried.