The ex-boyfriend of Sydney dentist Preethi Reddy, whose body was found in a suitcase on Tuesday, died after he deliberately drove his car into the path of a semi-trailer on Monday night, police have revealed.

Dr Reddy's body was found in her car, parked in Sydney's east, after she was reported missing when she didn't return home to Penrith on Sunday. Police said she had been stabbed numerous times.

The 32-year-old spoke to her family on Sunday morning about 11am, telling them she was planning on a late breakfast before heading home.

Dr Reddy and her ex-boyfriend, Tamworth dentist Dr Harshwardhan Narde, had gone to a hotel in Market Street in Sydney's CBD on Saturday night.