Kim Zolciak's Daughter Brielle Biermann Didn't Invite Kroy to Wedding

Brielle Biermann is preparing to walk down the aisle, but her adoptive dad Kroy Biermann won't be giving her away ... 'cause TMZ has learned he wasn't invited to her nuptials.

Sources with knowledge tell TMZ ... Kroy did NOT receive an invitation to Brielle's November wedding to fiancé Billy Seidl.

We're told Brielle and Kroy are no longer close for various reasons, and their strained relationship has reached the point where he won't be included in her big day.

The wedding snub comes as Kroy's relationship with Brielle and her sister, Ariana Biermann, has fallen apart amid his bitter divorce from their mom, Kim Zolciak.

Brielle previously told TMZ she couldn't say whether Kroy would attend the wedding because she hadn't heard from him in a while and had no idea what he planned to do. She also said she thought Kroy needed help and wasn't happy with his recent interactions with Kim.

Now, we're told Kroy won't be there ... because he never received an invitation.

Ariana previously told us she and Kroy are no longer speaking. She said the sisters tried for a long time to maintain a relationship with him outside the divorce drama, but it ultimately wasn't working.

Ariana called the family's situation heartbreaking and said watching the latest court filings and motions play out has been "insane."

Kroy adopted Brielle and Ariana in 2013 after marrying Kim. The estranged couple also shares four younger children.

As we first reported, Kroy was recently awarded temporary primary physical custody of the couple's four minor kids as his contentious divorce from Kim continues.