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Preston, 59, was arrested and charged with Ms Fan's murder yesterday. He was also charged with breach of a protection order in relation to the fatal November attack.
He appeared in the Wellington District Court before Judge Kevin Glubb today.
Ms Fan, who has two children with Mr Preston, was found stabbed to death in her Miramar home by concerned friends, two days after she died.
Police believe her killer had been wearing a disguise, and could have left in different clothes to what he entered her Brussels St home in on November 8.
Ms Fan and Preston's children are aged 8 and 9.
Last night, Ms Fan's boyfriend at the time of her death Tani Hoyhtya, told the Herald from Vietnam news of an arrest had come as a relief.
"It's happy news, I've been waiting for so long."
Mr Hoyhtya, who works for the United Nations, had decided to propose to Ms Fan and move to New Zealand to start a family with her.
Relocating in September would now be bitter-sweet, he said.
Police said this morning in a statement the investigation into Ms Fan's death had been complex and involved many phases.
"Our motivation throughout has been to bring justice for Mei and her children and they have remained at the forefront of investigator's minds."
"The past five months have been a very difficult time for the family and the Operation Brussels team is pleased to have reached this milestone in the investigation."