National Portrait Gallery director Sandy Nairne said Heldens had offered "a quiet but evocative study".
BBC: Wim Heldens wins 2011 BP Portrait Award
2.
Mr Nairne said it was an "exciting moment" to display the first commissioned public portrait of the duchess.
BBC: Kate portrait: First painting gets mixed reviews
3.
Sandy Nairne, former Director of Programmes at the Tate who oversaw the operation, also emphasises the Tate's working relationship with the appropriate authorities.
BBC: NEWS | Programmes | This World | How the Tate found its Turners