"The day I met you, my life changed. Thank you my love" she captioned the sweet post.
Khloé and Tristan began dating in September 2016, before it was reported in September that the couple were expecting their first child together. Tristan also shares a 1-year-old son, Prince Oliver, with his ex-girlfriend.
“This is something Khloé has wanted for years and years and yet it’s more than that: she didn’t want it unless she was in the right relationship for it," a source told PEOPLE. "She never let it happen with Lamar, intentionally, and she never considered it with James or French or anyone else she has seen."
“But this is such a wonderful moment for her: not only is she going to be a mother, she is going to be raising a child with a man she truly loves,” the source added. “Everyone is over the moon for them both.”