"My first born son is gone from me, dying from an overdose on his 29th birthday," Feherty posted on social media ... "Bless his sweet heart, I will fight on."

Shey died on July 29th. Funeral services are set for Tuesday.

The former PGA golfer has also battled substance abuse himself and previously said alcoholism and mental illness run in his family.

In lieu of flowers, the family is asking mourners to donate to the Center for Addiction and Recovery Studies.