Wilanne Stangel spotted an Ancestry.com message board posting about her dad, William J. Stangel.
"It was about a 3-year-old listing. It was a man who was looking for information about his father, William James Stangel."
Her response to Rolf "K.C." Stangel led to the realization that William Stangel had fathered them by different mothers. In the more than four years since the discovery, the Stangels have located two more half-siblings they hadn't known about and found records of at least 10 marriages involving their father, who died in 1974.
"We're at the point now where we're continually looking," said Wilanne Stangel, who is 48 years old and works as a librarian at Villa Madonna Academy. [Link]
[Thanks, J. Hansen!]