Alec Baldwin has honoured his father in a touching post on social media, exactly 36 years after his passing.

The Departed star, 61, took to Instagram on Monday (15Apr19) to post a pair of old photos of his dad, Alexander Rae Baldwin, Jr., and reflected on how he struggled to find a replacement father figure when the former high school football coach died in 1983.

"My father was a uniquely caring, dedicated, stern, smart and, at times, funny man who served as a public school teacher and coach for 28 years until his death at age 55," Alec wrote in the accompanying caption.

"Beyond missing those who are no longer with us, beyond wondering where they have gone and how life might have been if they had lived longer, the loss of a parent sets in motion the 'orphan clock.' The time when, after both parents are gone, one is an orphan in the world. With no one alive to parent you, which is a wondrous and vital calling."

"My mother is still alive, but the death of my father effected (sic) me tremendously and set me on a course of seeking other men to advise me. To care for me. Mentor me," he continued. "No one has quite filled that position."

"A mother, a father, under the best of circumstances, though never perfect ones, are irreplaceable," concluded Alec, who is one of six kids. "I miss you, Dad."

The actor's heartwarming tribute emerged just under a week after he and his wife Hilaria endured their own tragic loss, as the fitness instructor suffered a miscarriage during her first trimester.

The baby would have been a younger sibling for the couple's four young children, as well as Alec's 23-year-old daughter Ireland, from his previous marriage to Kim Basinger.