"Oh Jesus Christ," Ms Klune replied.

"How do you kill the love of your life? No way."

The court heard that Ms Klune, now a Brisbane factory worker, was told by Gerhard that she would inherit his Brisbane home.

But the couple were having difficulties and he'd asked her to move out.

Mr Funch suggested to Ms Klune she had returned to the house and used a key hidden under the washing machine in the outside laundry to access Gerhard's home.

She denied it.

A kiss on the cheek as her dropped her off at work a few days before he disappeared on January 7, 1999, was the last time she saw him, Ms Klune said.

The pair had arranged to have dinner at the Breakfast Creek Hotel - but Gerhard never showed up for the date.

Ms Klune said she called and went to the house but there was no answer. She never saw him again.

Earlier, the court heard Gerhard's cash-strapped nephew, Wagner, was regularly nagged about his wasteful ways by his uncle.

Wagner owed Gerhard about $84,000 and was in a difficult financial position, the court heard.

Ms Klune told the court the pair were always arguing.

"Gerry wanted him to change his lifestyle," she said.

"He wanted him to save some money (and) not to go out (so much)."

Gerhard was last seen riding a motorcycle after working on his prized yacht on January 7.

Neither his body nor the motorcycle has ever been found.

On Monday, Wagner pleaded not guilty to killing Gerhard in the garage of his uncle's home in January 1999.

Crown prosecutor Philip McCarthy said Wagner, who was the executor for Gerhard's will, made changes to it in the months before his uncle's disappearance.

A witness had also come forward with claims that Wagner told him he'd "knocked his uncle off" and got away with it, the prosecutor said.

The witness, who can't be identified for legal reasons, said Wagner told him he had cut and hacked his uncle's body to pieces with a knife and disposed of it in locations in the Glass House Mountains.

The trial continues.

AAP