Sculptor Rodin called his lover Gwen John 'God's little Artist' but until now the Welsh painter has not been recognised for her religious art.
But an exhibition of work painted as John converted to the Roman Catholic church aims to change that perception.
Birmingham's Barber Institute is showing some of John's series of nuns' portraits in its first summer show.
Institute director Prof Ann Sumner said she wanted to show the impact of John's conversion on her art.
The exhibition concentrates on Pembrokeshire-born John's commission from a French convent, which occupied her for eight years during the turbulence of World War I.
Prof Sumner said: "While Gwen John has gradually been recognised as one of the most important female artists of the first half of the 20th Century, her spirituality and its effect on her art is an area that has, until now receives scant attention.
"This exhibition is a wonderful opportunity to redress that, as well as to examine one of the most popular paintings in the Barber collection and explore a fascinating story about a very individual artist."
John, who grew up with her famous portrait painter brother Augustus John in Haverfordwest and Tenby, was commissioned by a convent at Meudon, outside Paris to paint its 17th Century founder Mère Poussepin.
The artist moved to the town in 1911 to be near ageing sculptor Auguste Rodin for whom she was a model and former lover.
Their affair was now over and John, who grew up an Anglican in her native Wales, found the break-up hard to accept and turned to the Catholic Church for comfort.
For her first Mère Poussepin painting, John used a photo from a prayer card.
But she was later asked to paint as many as seven more - one for each cell of the convent, and for those it is thought a contemporary nun was asked to pose.
Four of the portraits - each with its own maturity - are hanging in the Barber show - one the institute's own, the others are on loan from Southampton, National Museum Wales, and the Tate.
"Ironically," said Prof Sumner, "the convent only took one of the Mère Poussepins which so dominated John's output for that decade, and then they sold it.
"Of course, they were not to know how famous she was later to become".
The Barber show also features sketches in pen and the resulting watercolours that John occupied herself of parishioners at prayer as well as commentary on the spiritual aspect of some of her works by former nun Tessa Frank.
The Reunited exhibition includes many items from private collections - some which have never been on public view.
Prof Sumner said she also wanted to show the depth of Gwen John, so often shadowed in artistic terms by her brother Augustus.
Personal items including John's crucifix, her sewing box, a Madonna and child Dresden statue which was found buried beneath her Meudon home, and even the linen shirt which she painted in are also on show, alongside portraits of both Rodin and her brother.
The Barber Institute was founded by Lady Hattie Barber. Prof Sumner is its first woman director after moving there from National Museum Wales last year, and now she is staging its first exhibition by a woman artist.
"I'd like to think Lady Hattie Barber would be very pleased, " said the director.
Gwen John, Mère Poussepin and the Catholic Church is at the Barber Institute, University of Birmingham until 21 September 2008.