Boston Celtics guard Marcus Smart posted a touching tribute to his mother, Camellia, on Monday night, one day after she lost her battle with cancer.

"I feel like I'm suffocating and the person who helps me get through things [has] left me but I know [you're] in a better place with no more worries, no more hurt, no more sadness or pain," Smart wrote in a note posted to Twitter. "Hate to let u go but I thank god for allowing me to have one of his [angels] to call my mom."

Smart revealed in April that 63-year-old Camellia had been diagnosed with bone marrow cancer, but she implored him to focus on Boston's playoff run. Smart, returning from a thumb injury in the opening round, helped the Celtics take the Cleveland Cavaliers to seven games in the Eastern Conference finals.

Smart often wrote "Mama's Boy" and "I fight, you fight" and "F Cancer" on his shoes during Boston's playoff run.

Even after signing a four-year, $52 million extension with the Celtics over the summer, Smart admitted his focus had been largely on his mother's health.

Smart's heartache was evident in his message posted Monday night.

"Words can't express nor is there enough time in the world to tell u how much I love and miss u," Smart wrote. "So until we meet again I say R.I.P. To the strongest woman I know, Camellia Smart, my mom."

Smart's older brother, Todd, lost a long battle with cancer at the age of 33 in 2004, when Smart was just 9 years old. Since reaching the NBA, Smart started his own YounGameChanger Foundation, which strives to help young cancer patients. Smart routinely visits Boston hospitals to chat with kids battling cancer.

The Celtics open training camp Sept. 25 in Boston.