Rob Kardashian posted a heartfelt Instagram message to his fiancée, Blac Chyna, for Mothers day. This is just days after the couple announced they are expecting their first child together. Kardashian wrote "And last but not least happy mamas day to this beautiful mama," He continued to praise his new fiance by stating "I fell in love with her immediately because of how great of a mom she is and now I'm looking forward to starting a family with her! Thank you Chy for everything you do for me." Blac Chyna already has one son, 3-year-old King Cairo Stevenson, with her rapper ex-boyfriend, Tyga who is Kylie Jenner's current boyfriend .