Natasha Richardson, Liam Neeson Natasha Richardson, Liam Neeson

It's been nearly five years since Natasha Richardson tragically died in a skiing accident, but her widower Liam Neeson says it still doesn't feel real.

Speaking with Anderson Cooper for an interview that will air Sunday on 60 Minutes (7/6c on CBS), Neeson says after all this time, her death "was never real. It still kind of isn't."

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Neeson and Richardson were married for nearly 15 years and had two sons together, Micheál and Daniel. "There's periods now in our New York residence when I hear the door opening, especially the first couple of years," the actor says. "Anytime I hear that door opening, I still think I'm going to hear her."

Richardson died in March 2009 at the age of  45 due to head injuries suffered in a skiing accident in Montreal. During the interview, Neeson recalls arriving at the Canadian hospital where doctors told him his wife was brain dead. "She was on life support," he says. "I went in to her and I told her I loved her, said, 'Sweetie, you're not coming back from this, you've banged your head.'... She and I had made a pact, if any of us got into a vegetative state that we'd pull the plug... that was my immediate thought... 'OK, these tubes have to go. She's gone.'"

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Richardson's heart, liver and kidneys were then donated. "It's terrific," he says. "I think she would be very thrilled and pleased by that."

Still, Neeson grieves his late wife five years later. "It hits you. It's like a wave," he says. "You just get this profound feeling of instability... the Earth isn't stable anymore, and then it passes and it becomes more infrequent , but I still get it sometimes."

Watch an excerpt of Neeson's interview below: