The 57-year-old singer and musician wished Momoa a happy birthday in an Instagram post Sunday.
Kravitz shared a photo of himself with Momoa that was taken by photographer Mark Seliger.
"Happy Birthday, @prideofgypsies. I'm proud to call you my brother. One love. One family," Kravitz captioned the post.
Momoa responded with love in the comments.
"love u madly," he wrote, adding "thank you very much" in Hawaiian.
Momoa and Bonet married in October 2017 and have two children together, daughter Lola Iolani, 14, and son Nakoa-Wolf, 12.
Kravitz discussed his friendship with Momoa and Bonet in the November issue of Men's Health magazine.
"People can't believe how tight Jason and I are, or how tight I still am with Zoe's mom, how we all relate," Kravitz said. "We just do it because that's what you do. You let love rule, right?"
"I mean, obviously, after a breakup, it's work -- it takes some work and time, healing and reflection, et cetera," he added. "But as far as Jason and I? Literally the moment we met, we were like, 'Oh, yeah. I love this dude.'"