Bruce Jenner -- I'm Proud of Kendall Jenner's Boobs

Kendall Jenner doesn't need a bra ... because her own father fully supports her breasts.

Sources close to Bruce Jenner tell TMZ, he 100% backs his 18-year-old daughter's decision Tuesday to expose her nipples on Instagram. As far as he's concerned, she's a fashion model ... and that's what fashion models do.

Soon after Kendall posted the pic for her 7 million followers, Bruce began defending his daughter ... saying she's a "wonderful kid and a great daughter" ... and insisting he's proud of her no matter what she does.

Just so we're all clear ... Kendall turned 18 on November 3rd. We're proud of her too.