David McCallum will forever mourn the loss of his son, Jason, who died from an accidental overdose in 1989.
The NCIS star rarely talks about the tragic death but has opened up on an occasion to express his heartache over the tragic situation.
Jason - who was adopted by David and his then-wife, Jill Ireland when he was young - was living in California at the time of his death and was found at his home in Laurel Canyon, Los Angeles.
He had been struggling with an addiction to drugs and was just 26 years old when he died.
Speaking to the Belfast Telegraph about his son, David said: “You never come to terms with the death of a child. The pain is very real, but it's like an ache that turns into anger.
"At the same time, there’s a frustration that you couldn't really have done anything about it, which makes it even worse."
The Scottish-born actor added: "In the final analysis, he had the life he had. You just have to accept it."
Not that the pain ever goes away. David has since said: "The tragedy still haunts me. Jason got in with a certain type of showbusiness people and there was a drug culture going on and it killed him.
"I will always regret not being able to help Jason. He was one of the most wonderful people you could hope to meet."
David - who has played the character of Donald ‘Ducky' Mallard on NCIS since the pilot episode - later told The Mirror that there was a source of comfort after his death, however, as he discovered he had a grandchild.
"I had some fantastic times with him and his lasting legacy is a son, Tory, who has become friends with my sons.
"I didn't know Jason had posthumously become a father until a card arrived in New York a few months after his death.
"It was from a young woman who had been living with him, telling me they had a son. He's in his early 20s now and I hope he turns out to be as fine a person as his dad."
David and Jill - who had two other adopted children - divorced, and she went on to marry actor Charles Bronson and he met his current wife, Katherine Carpenter.
They had two children together and remain a married couple to this day.
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