Oops! Miranda Lambert Doesn't Thank Fiance Blake Shelton at Grammys

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Dag nabbit!

Miranda Lambert pulled a Hilary Swank at Sunday's Grammy Awards.

While accepting a trophy at the L.A. bash, the "House That Built Me" singer made a glaring omission among her many thanks: Her fiance Blake Shelton, who beamed from the audience!

"I forgot!" a mortified Lambert, 27, explained in the press room backstage.

Lambert and Shelton, 34, plan to tie the knot this spring.

"I'm looking forward to getting married -- just doing it," she told UsMagazine.com last year. "Just taking that next step and becoming a woman and moving on in life."