The mother of a 3-year-old boy has been charged with capital murder after her son died at a Dallas hospital. 

McKinney PD confirmed that Chelsea Berg, 30, was arrested on Monday. Her boyfriend, 30-year-old Christopher Alexander, is also charged with capital murder.

Dallas County Medical Examiner records show that Berg's son, Dawson Zamora, died at Medical City Dallas on Sunday, December 7. 

Dawson's father, Dahrian Zamroa, also confirmed his son's death in a social media post. Sunday was Dahrian's birthday.

"His gift to me was his final breath and we are now forever interlocked with my birth and his death. He held on to spend one last birthday with me and refused to go until then," Dahrian Zamora wrote on Facebook.

Berg and Alexander were first arrested in October and charged with injury to a child, a first degree felony. Alexander was also charged with tampering with evidence. 

Berg had been out of jail on bond until she was arrested again on Monday. Alexander has remained in custody at the Collin County Jail. 

The case began when officers responded to Medical City McKinney hospital on Oct. 14 regarding a 3-year-old brought to the emergency room, police said. 

Medical staff said the child had serious injuries and was unresponsive when he arrived at the hospital. 

According to an arrest affidavit, Alexander, who brought the child to the hospital, claimed he found the boy after hearing a thud from another room. The boy had severe brain trauma, bleeding in the brain, bruising all over his body as well as wounds on his chest, stomach and rear. 

Hospital staff told police that the boy's injuries did not match up with Alexander's explanation. 

Berg told police she left her son with Alexander on Oct. 14 before heading to work. She said he called her after lunch saying he was panicked and was taking him to the hospital, according to the affidavit.

Berg was shown pictures of her son and was adamant that he didn't have those injuries when she went to work that same morning.

Police obtained warrants for Berg and Alexander's phones, which revealed text messages talking about bruises and injuries to the boy over a month prior to Oct. 14.