"Watching you evolve into the partner, friend, son, and father you are today has been so fulfilling," Kylie, 21, wrote lovingly.
"My real life bestie & hubby all wrapped into one. I love you and I’m so so proud of you," the Keeping Up with the Kardashians star said.
"Happy happy birthday ?? let’s f**k around and have another baby," she concluded.
As OK! readers know, this isn't the first time Kylie has mentioned giving baby Stormi, 14 months, a sibling! On February 3, she captioned an Instagram post, "Baby #2?"
Also, a source told Us Weekly in December 2018 that “there is no question that they want to give Stormi a sibling and way sooner than people expect." While Kylie kept her first pregnancy top secret, there is no telling if she will reveal the news the second time around!
Travis also took to social media to share his blessings on his big day. "Going ham all day," he wrote on Instagram alongside a photo of birthday balloons. "Blessed to see another year with family and friends. Love everyone that helps me in my life. Thank you God."
Do you think Kylie and Travis will announce the pregnancy of their second child the second time around? Let us know in the comments below!