DUCK DY­NASTY’s  witty Uncle Si Robert­son is a laugh a minute on the A&E hit, but few fans know of his secret heartbreak as his family battled depression and suicide.

The warmhearted Rob­ertson clan has smashed TV records, attracting a phenomenal 12 mil­lion viewers to the cable show, which revolves around their homespun wisdom and the unlikely way they’ve earned mil­lions – selling duck calls.

And “Duck Dynasty” patriarch Phil Robertson helped boost the family’s fortune to more than $75 million with the success of his tell-all memoir, “Happy, Happy, Happy.”

BUT Vietnam vet Si, 65, went through hell before achieving incred­ible success. Si married his wife Christine in 1971 even though she believed she couldn’t have chil­dren.

Miraculously, Christine gave birth to their daugh­ter Trasa in 1975. But when she was pregnant with their son Scott in 1977, the family faced a ter­rifying ordeal.

“Doctors told Christine there was a serious prob­lem with her pregnancy and broke the news that her fetus would prob­ably die,” Si reveals in his fascinating new book “SI-COLOGY 1: Tales & Wisdom from Duck Dynas­ty’s Favorite Uncle.”

“When Scott was born, Christine kind of went into a shell because she was convinced he wouldn’t survive,” writes Si.

The baby’s liver wasn’t functioning properly, and they learned later that the problem had damaged part of his brain.

“Christine be­came depressed and was really battling her emotions,” confides Si, adding that “Scott was suicidal from the time he was about five years old. His behavior was really erratic as a child.”

At the age of 11, the young­ster destroyed everything in his room. And when Christine went to check him out, she found her be­loved son poised to leap out a second-story window.

“I can’t go on,” Scott pleaded, according to the book. “…Make the pain go away.”

The family soon learned that Scott was suffering from Asperger’s syndrome, a form of autism.

But thanks to excellent treatment, Scott became a good student, married and now has a family of his own.