Post Malone's understandably devastated over the shocking death of his friend and fellow rapper, Mac Miller ... because like he says -- it really f***ing sucks.
We talked to Post in Beverly Hills Friday shortly after the tragic news of Miller's death broke ... he tells us he's really going to miss him, and that he was nothing but a beautiful, sweet and loving guy.
The rapper says he listened to Mac's music growing up and was greatly inspired by him ... and the 2 even had plans to make an album together. Post fights back tears telling us about some of his favorite memories ... like kicking ass with Miller at beer pong.
We broke the story ... Miller was found dead in a bedroom at his San Fernando Valley home from an apparent overdose.
His family released a statement saying, Mac "was a bright light in this world for his family, friends and fans. Thank you for your prayers."
RIP