In 2011, Donald Trump gave an interview to Greta Van Susteren on Fox News. He said (quote courtesy of the New York Times):
A birther is a person that wants — these are great Americans in many cases, in most cases — they want to see the president was born in this country. They want to see the president actually has a birth certificate.
The Times article linked above speculates on how Fox News might change now that Roger Ailes has stepped down.