I'm a big Bluetrix shipper. It's a shame they never made it canon, or introduced Trixie to Prince Blueblood, or brought him back in the series. Here's how I thought it would go down.

In the finale 'To Where and Back Again', Starlight and Trixie just learn that Twilight and her friends were replaced by changelings. Outside Twilight's castle, they meet with Prince Blueblood. He was forced to come to Ponyville alone seeking Princess Twilight's help after learning his Aunts Celestia and Luna have been captured, only to learn it was too late. He becomes part of the group. When topic of the the Crystal Empire comes up and Thorax shows up, Blueblood starts screaming along with Trixie.

Change the size, darken the colors a bit...and VOILA!