The RCMP will charge a man with first-degree murder in the death of Sabrina Patterson on Monday afternoon. (CBC)

The former boyfriend of a woman who went missing last October has been charged with first-degree murder in her death.

Fred Prosser has been charged in the death of 25-year-old Sabrina Patterson, whose body was found in a wooded area in Shenstone, a small community in southern New Brunswick.

Prosser, who had two children with Patterson, has also been charged with three counts of sexually assaulting Patterson, and two counts of breaching an undertaking.

He has already pleaded not guilty to assaulting Patterson, stealing her cell phone, and breaching an undertaking to have no contact with her.

Patterson was reported missing on Oct. 31, 2010. Her body was found in the woods near Shenstone on Nov. 6.

Prosser, 32, was also reported missing on Nov. 1, and was found at his father's home in Shenstone three days later.

The new charges cover the period of Oct. 29 to Nov. 4.

RCMP Cpl. Dan Roy said it took three months to lay the murder charge because it was a complex investigation.

"We've assembled a team of investigators that have worked on this investigation and has led us today to a charge of first-degree murder," he said Monday. "It's a charge that was reviewed by the provincial Crown and approved as well which has brought us to a successful laying of charges today."

The court was crowded with friends and family of Patterson, many wearing purple T-shirts bearing her picture and the words 'Always in our hearts.'

Prosser is scheduled to return to court to face the new charges on Feb. 28.