Highlights of the upcoming auctions in Beijing include a Qing Dynasty (1644-1911) enamel cup. [Photo provided to China Daily]

The letter, titled Jushi Tie, which translates as "a letter on happenings", is written in kaishu, the regular calligraphic script. It will be auctioned at a China Guardian Auctions night sale.

The letter was once part of the collection of the Belgian couple Guy and Myriam Ullens, who sold it in 2009 for 108.64 million yuan ($17 million) at a Poly Auction sale in Beijing.

China Guardian hasn't revealed the current seller's identity.

Guo Tong, who heads the company's Chinese paintings and calligraphy department, says it is "an old customer", and they hope the letter will boost the sluggish Chinese paintings market.

Zeng isn't celebrated as a calligrapher.

However, he collected and studied calligraphic inscriptions on ancient bronze ware and stone tablets－it is said he had more than 500 pieces－which nourished his writing technique.