when was the actor revealed as "The Mother" in the Season 8 finale in  How I Met Your Mother born 
How I Met Your Mother (season 9):  Cristin Milioti, who was revealed as "The Mother" in the Season 8 finale, was promoted to a series regular, the only time "How I Met Your Mother" added a new regular cast member. Cristin Milioti: Cristin Milioti (born August 16, 1985) is an American actress and singer.
August 16, 1985)