CBS has confirmed that the actress shown in tonight’s episode is indeed the mother of “How I Met Your Mother.” I’ll be writing more about this later (much more). Congratulations to all involved for doing a great job of keeping it a secret.
From The Hollywood Reporter:
Identified only as "The Girl with the Yellow Umbrella," the actress playing the mother and set to figure prominently in the series' final season in Cristin Milioti. Speculation about who would be cast in the role has come up with nearly every female guest star to join the series -- though this is a first appearance for Milioti.
Red herrings have been par for the course since the series first started teasing the big mystery, but a CBS rep confirms to The Hollywood Reporter that Milioti is indeed the actress playing the future bride of Ted (Josh Radnor). No other details about her addition were available at the time.
Milioti is likely best known for her Tony-nominated performance in the stage production of Once, though her TV credits are many. She recurred as Johnny Sack's daughter Catherine on The Sopranos and became a top Google search in 2011 when she played a foil to Tina Fey's Liz Lemon in the 30 Rock episode, "TGS Hates Girls."
And while How I Met Your Mother may have introduced Milioti's character at the tail-end of the episode, at the conclusion of a montage showing the series' core five cast members en route to Barney (Neil Patrick Harris) and Robin's (Cobie Smulders) wedding, the show held of on introducing her to anyone more than the audience. Milioti and Radnor shared no scene in the episode.
Co-creators and executive producers Craig Thomas and Carter Bays have previously confirmed that official meeting of Ted and The Girl With the Yellow Umbrella will take place after the wedding, as the season eight premiere teased.