The last words an Oregon woman spoke to her family included a joke about being murdered, before she died while hiking with her boyfriend in 2009.

Julia Simmons, the mother of Rhonda Casto, shared what her daughter said with Maria Elena SLaines of Investigative Discovery's The Real Story, in an interview that airs on Monday.

Casto's last words to her grandmother and aunt before embarking on the Eagle Creek Trail along Oregon’s Columbia River Gorge on March 16, 2009, with Stephen Nichols were supposedly, 'He is either going to give me a ring or throw me off a cliff, ha ha ha,' Simmons said.

Nichols, who was first charged with murder in 2015 for Casto's death, instead pleaded guilty to criminally negligent homicide and coercion in May 2017, and was sentenced to three years’ of probation, with credit for 19 months of jail time.

Casto and Nichols shared a daugther, named Ava.

The last words Rhonda Casto (right) spoke to her family included a joke about being murdered, before she died while hiking with her boyfriend, Stephen Nichols (left) in Oregon in 2009

The plea deal for Nichols came after the Oregon Supreme Court ruled in March 2017 that a detective should have stopped interrogating Nichols when the suspect said he did not want to discuss Casto’s death.

The interview occurred shortly after Nichols’ February 2015 arrest at San Francisco International Airport, nearly six years after his partner’s death.

A Hood River County judge had ruled the statement inadmissible, but the state appealed to the higher court, and lost.

Nichols, who has maintained he had nothing to do with Casto's death, told People magazine, 'She was so happy' on the day of the hike.

When asked about what she allegedly said to her family that day, he said, 'The simple answer is I don’t think she ever actually said that.'

But Simmons paints a different picture, having previously told People, 'She was going to move out, but she was trying to get up the courage to do it.'

Simmons added: 'She was worried about not having enough money to support Ava.'

Nichols, then a recently divorced 30-year-old day trader, met Casto, a 20-year-old aspiring model, in 2005 after Casto's mother introduced them

Nichols was originally charged with murder in 2015, but that charge was dropped when he took a plea deal that landed him three years’ of probation, with credit for 19 months of jail time

On the day Casto dies, Nichols called 911 at around 6pm that night to report Casto's 100-foot-fall to her death.

He has said that he slid down the ravine toward her, and had to cross an icy creek to reach her body, but by the time he got there he collapsed on top of her, overcome with exhaustion and hypothermia.

The popular hiking destination has been the scene of other accidents in the past due to a few narrow sections that drop off on one side into a ravine.

The trail was even more dangerous that day due to a battering of sleet and hail that made the path treacherous.

Records show that several months before the incident, Nichols, then working as a day trader, increased Casto’s life insurance policy to $1 million.

Court documents show Nichols and Casto became romantically involved in 2005, according to The Oregonian.

Casto and Nichols reportedly both took out $1 million life insurance policies on each other shortly before her untimely death in March 2009

Treacherous path: The hiking trail where Casto fell to her death has a few narrow sections that drop off on one side into a ravine

In an interview with CBS' 48 Hours, Casto's mother, Julia Simmons, said that she was the one who introduced Nichols to her daughter while renting a room in his three-bedroom condominium in Portland.

Nichols was 30 years old and recently divorced, and Casto was 20 at the time.

'Everything about her was impressive,' Nichols said in the March 2015 interview, adding, 'and I just immediately fell in love with her.'

Before long, Casto moved into Nichols' home, and three years later they welcomed their baby daughter, who is now seven.

The papers reveal that the couple each bought a $1 million life insurance policy in late 2008 from MetLife and named each other as beneficiaries. Their daughter was named as contingent beneficiary.

Nichols eventually agreed to split the money with Casto's mother and with the estate of his daughter.

In the 48 Hours interview, Nichols said that after delivering their baby, Casto said she wanted to lose the baby weight so she could start modelling again, so the couple took up hiking.

Simmons said that in the weeks leading up to the fatal March 2009 outing to the Eagle Creek Trial, her daughter told her that Nichols had been trying to convince her to go for a hike for a month.

Nichols said that day started off as a nice day but the weather turned inclement as the couple were making their up the narrow, moss-covered trail

As they reached a particularly slippery portion of the pathway, Casto fell off the cliff to her death.

Nichols said he hiked down to the spot where his girlfriend came to rest and tried to give her CPR, but it was too late.

He would later claim that the 23-year-old mom was high that afternoon, was acting silly and running on the slick trail before disaster struck.

The Real Story with Maria Elena Salinas airs on Monday at 10.00pm Eastern on Investigation Discovery.