Wellington, Oct 4 NZPA - The sister of convicted murderer Clayton Weatherston says he will not appeal his life sentence.

Weatherston, 33, was jailed for a minimum of 18 years in September after a jury found him guilty of murdering his former girlfriend, Sophie Elliott, in January 2008.

His sister, Angela Muir, had visited him in prison and said he felt deeply remorseful.

"I believe he felt that all along," she told the Herald on Sunday.

"He is not a monster ..."

Her brother would not appeal his sentence, Ms Muir said.

Weatherston had admitted stabbing Ms Elliott 216 times, but tried to argue he had been provoked and has been widely vilified for his apparent lack of remorse.