Kong by Sotheby’s are low-quality forgeries.

He is determined to protect his father’s reputation, Phuong said.

“I’m really disappointed with Sotheby’s. They say they have the best experts to evaluate the authenticity of the artwork but this is not the first time they are selling fake Vietnamese paintings.”

Phuong claims three other Phai fakes were successfully sold by Sotheby’s on April 8.

Phuong’s contention is backed by two renowned collectors of Phai’s works – Tran Hau Tuan and Vietnamese-French Gerard Chapuis.

Phuong says he had sent a complaint to Sotheby’s but had not received any response.

Bui Xuan Phai, who died in 1988, is considered the greatest among modern Vietnamese master painters. He was known for his works depicting Hanoi’s Old

Quarters, which were often called Pho Phai (Phai’s quarters).

He was one of the “four pillars of Modern Vietnamese modern art” along with Nguyen Tu Nghiem, Duong Bich Lien and Nguyen Sang. He was posthumously presented the Ho Chi Minh Award, Vietnam’s highest award for artists, in 1996.

Until Saturday, the five pictures were still posted on Sotheby’s official website for auctioning tomorrow at the Hong Kong Convention and Exhibition Center for HKD120,000-200,000 (US$15,400-25,700).

Sotheby’s has so far not commented on the allegations.

Sotheby’s, founded in 1744, is one of the biggest auction houses in the world with annual turnover of about $3 billion.

The house holds the world record for most expensive work of art sold at an auction with Picasso's Garton a la pipe (Boy with a Pipe) bought by an anonymous client for $104 million in 2004.

Reported by Ngoc Luong