A depressed man.

Families can be complicated, especially when couples separate or there has been infidelity somewhere along the line. But, there are few situations quite as complicated as this man's family tree, after he discovered his son is actually his uncle.

TikTok user @stacks1400 made the devastating realisation after discovering his girlfriend, the mother of his child, had been having an affair with his very own grandfather while they were living with him.

"Found out my son was really my uncle," he said in a clip shared to TikTok. "My granddad was f***ing my girl the whole time we was staying with him."

The man shared the clip alongside the caption: "Can’t believe I expected more from a man that had a whole other family around the corner from my granny house," suggesting the granddad has a long history of infidelity in the family.

"I'm so sorry for you, I know it seems dark now. Get some time away for yourself. You didn't deserve this, but there is someone else out there for you," one supportive TikTok follower commented.

Another added: "Don't stop loving that young man, it's your time to stand tall in all this. Break the cycle and love that boy, regardless of what title he has."

After receiving an influx of well wishes from concerned followers, many questioned him for more details on how it could've happened without him knowing.

The man went on to explain that he'd picked up his girlfriend's phone while she went in the shower and discovered "years' worth of messages and pictures and explicit stuff."

In another video, Stacks promised he would continue to treat his son as his son, and their relationship wouldn't change just because he found out about his girlfriend's affair.