How did the Monarch Butterfly evolve?

It is believed that the Monarch Butterfly originally evolved in South America and then was split into different subspecies. Others believe it evolved in the "New World". Fossils of butterflies have been found that are believed to be 35 million years old. However, the Monarch and other milkweed butterflies aren't represented in the fossil records. This means there is no record of exactly where the Monarch Butterflies evolved from.