The Unsigned Masterpiece

Paul Jerome Barry is an American artist who attended the Chase School in Manhattan in 1901 and 1902. He fell in love with another student in the school, they married, and moved to Paris in 1903. His wife died in a fatal accident shortly after their arrival, but not before he had painted the best work of his life, her portrait. He found comfort and remarried. He struggled with disbelief in his own ability, an obsession with perfection, and the loss of his wife.
His fate was forever changed when met Lucas, a 12-year-old autistic boy in Normandy with savant syndrome and gave the boy the opportunity to paint. He brought Lucas's painting back to Paris, amazed by the work, which was in a new style like nothing he had never seen before. He put it in his studio and strove for the next 12 years to achieve its excellence. Unable to attain the result he was looking for; he fell into a depression. Lucas grew to be a man with a passion for painting and a secret. They meet again, but only after Lucas has lost his right arm in WWI. All of this is set in the artistic scene of Paris from 1900 to 1920.
Will Paul Barry succumb to his depression or find the will to continue? What is Lucas's big secret?