Your options are very limited.

First, you made a unsecured loan. There was no promissory note nor was there any collateral attached.

Second, he filed for bankruptcy. Technically speaking had he listed that $31k in the filings, you should have received notice from the US Bankruptcy Trustee informing you of the filing and your rights. I'm assuming you never received such notice, which will still allow you to deal with this. Had you received notice, you fall in the back of the line, after secured lenders.

Third, the whole family dynamics of this is limiting your options. You can try to speak with him and see what his intentions are but if you are not going to (1) follow up on investigating what happened at bankruptcy; or (2) pursue this with a civil action (is statute of limitations permit), you might as well suck it up and take it as a lesson learned. Unless he's such a scumbag, I'm sure he thinks about it as well and will someday try to make amends.

Good luck.