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Travis Kelce and his bro Jason made a lot of people do a double-take on their recent podcast with some love for Blake Lively ... the actress herself was among those taken aback, given her fallout with Taylor Swift .

Here's the deal ... the Kelce boys took a trip down memory lane on "New Heights," gushing over Blake’s movie breakout in 2005's "The Sisterhood of the Traveling Pants" ... saying how their "friend" totally crushed it. Play video content

A source with knowledge tells TMZ … Blake was pleasantly surprised by the comments … and she appreciated the kind words from the duo. Blake knows ‘Sisterhood’ has a loyal fan following -- which clearly includes the brothers … and it’s one of her favorites, too.

The admiration from the brothers comes on the

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