Ms Uhlirova could not say what the portrait of Russell was worth, or who the private collector was, but did reveal that the museum had been forced to take extra precautions to ensure the safety of the prized artwork.
"We've had to take out special insurance and it has to be locked in the [fire-proof] vault every night," she said.
This year marks 150 years since Henry Robert Russell established Waipukurau in his pursuit of a "socialist utopia".
Born in Dunfermline, Fife, in Scotland, on coming to New Zealand Russell bought part of the Waipukurau Block in 1853 and built his homestead, Mount Herbert. In 1856 he built the Tavistock Hotel for his guests and in 1867 bought the 84ha block known as the Native Reserve where he founded Waipukurau as a "model village".
Ms Uhlirova said Russell was an important, but polarising figure.
"People say he wanted to be the 'king of the village' but from my research, he wasn't a bad man. He donated the land for the hospital and school."
Along with his portrait, Ms Uhlirova said Russell would figure prominently at the exhibition with an information board detailing his life. Volunteers had painted the Tavistock Hotel on a wall of the exhibition hall and created figures of Russell and Mary Gow (nee Scrimgeour), the "mother of Waipukurau" who ran the Tavistock Hotel for decades.
A map of Waipukurau had been drawn on the floor of the hall. Children will be able to place wooden replica buildings along Ruataniwha St after researching the locations.
"So there's an interactive element to the exhibition," said Ms Uhlirova.
The museum had also secured the Alastair Jones Collection of historical photographs for the exhibition and digitised its Waipukurau Hospital photographic collection which will be displayed on screens.
CHB Settlers Museum chairman Hans Dresel will start proceedings with a welcome at 2pm this Sunday, before CHB Mayor Alex Walker makes an address and officially opens the exhibition. At 2.30pm there will be the book launch of Fading Memories: Waipukurau - Our town from 1920 to 1935 by the late Jessie MacKenzie Hamlin, presented by her son, Ken Hamlin.
The public is welcome to attend and encouraged to dress in period costume. Vintage cars would be used as taxis to ferry people from Waipukurau to Waipawa for the opening, Ms Uhlirova said.
"But only the special guests," she laughed.
Long-awaited details about other events later in the year celebrating Waipukurau's 150th anniversary have been announced.
A community group led by CHB district councillor Gerard Minehan had been brought together to plan events to celebrate the milestone.
"The itinerary of events will largely take place across Labour Weekend and be built into the Central Hawke's Bay Spring Fling programme and will ensure both the locals and visitors have a chance to be involved in marking this wonderful occasion," Mr Minehan said.
A powhiri will be held at the Waipukurau Pa site near Russell Park for invited guests on Friday, October 20 to start the celebrations. The evening will include a special reveal to celebrate, educate and acknowledge Maori history of Waipukurau and this piece will then be gifted long-term for the wider public to enjoy.
A free parade through the main streets of Waipukurau on Saturday, October 21 will feature vintage vehicles and machinery and period costume.
On the Saturday evening Waipukurau Primary School is holding a gathering of past and present staff and students. The evening will include cutting a cake, drinks, nibbles and lots of laughter and reminiscing. More information about this event can be found at the school office.
To close the celebrations on Sunday, October 22, a special high tea will be hosted by the Central Hawke's Bay Tea Party ladies group on the front lawn of George and Beth Winlove's homestead on Gaisford Tce. The event will be used as an opportunity to mark the anniversary and fundraise for Central Hawke's Bay Cancer. Tickets go on sale for this event closer to the time.
Mr Minehan said the diverse offering of events was a great way to celebrate Waipukurau's anniversary.
"We want to welcome the whole community to help in creating and celebrating 150 years history of Waipukurau and Waipukurau Primary School (1867-2017). We are keeping costs as low as we can, however there are the usual costs involved in running events like these, and we welcome any person or business who would like to contribute to the celebrations to feel free to get in touch."
Mr Minehan was excited about the number of events planned and thanked people who had so far come on board in giving their time, advice, donated goods and energy.
"We greatly appreciate all that people have done so far and look forward to celebrating 150 years both in March at the exhibition opening and book launch, and in October over Labour Weekend."