If I remember correctly, this portrait had been on loan to the gallery from the private owner for sometime, but now the gallery permanently owns it.
From the BBC:
Lady Dacre, and her son, Gregory Baron Dacre, by Hans Eworth, is described as “one of the finest works to be painted in Britain in the mid-16th century”.
The gallery paid just under £1m to secure the painting, following a public appeal for donations.
Sandy Nairne, director of the National Portrait Gallery, said: “It is a great acquisition for the nation.”
Painted in 1559, the portrait is widely acknowledged as one of the great gems of Tudor portraiture.
Full article (with image)