An art expert was unfairly sued after he concluded that his own grandfather had created a Western-theme painting bearing the name of a better-known artist, a jury ruled.

Jurors on Monday awarded Steve Seltzer nearly $21.4 million in damages in the dispute over the watercolor “Lassoing a Longhorn,” supposedly signed by the painter C.M. Russell in 1913. It is owned by Steve Morton, an heir to the Morton Salt fortune.