Rob Kardashian was feeling "so thankful" for former fiancee Blac Chyna on Mother's Day. The 30-year-old reality star marked the occasion by dedicating a sweet post and video to Blac Chyna and their 6-month-old daughter, Dream, on Instagram. "Happy mama's day to the mother of my only child @blacchyna :)," Kardashian captioned the post on Instagram. Blac Chyna is also mom to 4-year-old son King Cairo with ex-fiance Tyga. The video, which is set to the MAJOR. song "Why I Love You," features moments from the 29-year-old star's pregnancy and Dream's birth, and sweet shots with King and Dream. "I am so Thankful for our beautiful baby girl and so Thankful for YOU and never thought I could be this happy so thank you for giving me Her," Kardashian wrote. Kardashian and Blac Chyna ended their engagement in February following a highly-publicized split in December. Sources denied in April that the pair are back together after they had a flirty night out in Los Angeles. "They are co-parenting and independently working on themselves but they're more cordial now than they have been, which is why they hung out recently," an insider told E! News. "But by no means are they back together." Blac Chyna said in the April issue of Cosmopolitan South Africa that she's "in it for the long haul" with Kardashian. The model shared a cute picture with King and Dream on Sunday, writing, "Happy Mother's Day."