Stay with us. We know that headline is awful confusing, but stay with us.
In a very strange but not unheard-of medical case, the unborn twin of an adult man in the US has been found to be the genetic father of his one-year-old child.
After the 34-year-old and his wife had treatment at a fertility clinic, they came to learn that their child - born last June - did not have a blood type that matched either of its parents. They then did an at-home paternity test and realised that the man was not the biological father of the child.
Initially, the couple - pretty upset at this stage, as you can imagine - assumed that the fertility clinic had mixed up the sperm samples and used the wrong sample to impregnate the woman. However, after further testing it was later revealed that the genes in the man's saliva didn't match those in his sperm.
Here's where it gets really weird.
After in-depth 'genetic ancestry' testing, it is thought that the man absorbed cells from another foetus in the womb. His sibling was never born, and was believed to have been miscarried in the early stages of pregnancy - but it was enough to affect the adult man's gene pool. So much so, that his never-born twin brother is technically the father of 'his' child.
It is believed to be the first reported case of a paternity test affected by what is known as a human chimera - when cells absorbed in the womb cause a person's own genetic make-up to be altered.
The Washington-based couple have decided to remain anonymous for obvious reasons.