The supermodel just posted video of her hubby in a bathroom on her social media page, showin' off his fit bod and his latest Brady Brand boxer briefs.

Tom appears to be timid in the clip -- but Gisele was clearly loving putting him on camera, asking the Tampa Bay Buccaneers star about his skivvies over and over again in the quick vid.

"Hey new underwear!" Gisele said while laughing. "Let me see. Let me see your new underwear. Is that Brady Brand?!"

Tom, with some sly hand placement to make sure the camera didn't capture too much of his body, eventually threw a towel over his wife's phone -- before the video ended.

As you know ... Brady ventured into the retail industry at the beginning of this year when he launched his own Brady Brand clothing line, and it seems the next item he's lookin' to hawk is underwear.