There was a surprising cameo in the Game of Thrones season 8 premiere as It's Always Sunny in Philadelphia star Rob McElhenney appeared in a scene. After a 20-month hiatus, the HBO series returned for what will be the final six chapters intended to close out the epic fantasy drama. The premiere was packed with significant moments, many of which have been anticipated for years.

The episode, titled "Winterfell," featured the arrival of Daenerys and her armies to Winterfell and the long-awaited reunion between Jon Snow and his siblings. Back in the South, Euron Greyjoy returned to King's Landing with the Golden Company, just as promised. While Euron tried to charm his way into Cersei's private chambers, Theon went on a rescue mission to save Yara, sneaking aboard Euron's ship, the Silence, and successfully retrieve his sister. Before freeing Yara, Theon killed a few unsuspecting men left on the ship. The first kill was a very familiar face to It's Always Sunny fans.

Related: Game Of Thrones: Why Jon Snow Is The Rightful Ruler Of Westeros, Not Dany

The man that was killed on the deck of the Silence was Rob McElhenney, as confirmed by the actor's Instagram. McElhenney's character took a quick arrow in the back of the head through the left eye. The blink and you'll miss it cameo caught many fans off guard, and some missed the appearance altogether.

The creator and star of It's Always Sunny is reportedly friends with Game of Thrones showrunners David Benioff and D.B. Weiss. The showrunners even wrote an episode of It's Always Sunny in 2013. Unfortunately, this wasn't a "The Gang Goes to Westeros" situation featuring the entire cast but there was also another surprise cameo in the rescue sequence. Silicon Valley actor Martin Starr was also one of Euron's men killed aboard the ship.

McElhenney and Starr joined Snow Patrol's Gary Lightbody, Coldplay's Will Champion, Sigur Rós, and Ed Sheeran as celebrities who have cameo appearances on the hit HBO series. In fact, one of the Game of Thrones' premiere's callbacks was to the latter: one of Bronn's female companions brought up a "ginger" named Eddie who got caught up in the attack by Daenerys' army, revealing Eddie's fate along with his now missing eyelids.

With only five episodes left, it will be interesting to see if the showrunners have any more surprising cameos planned. It's no question why celebrities would want to jump at the chance of appearing in a series as popular as Game of Thrones. Even though the celebs tend to meet a very dark fate, it would be something to brag about. With Game of Thrones nearing the end of its run, keep those eyes peeled for any more familiar faces.

Next: Game Of Thrones: What Arya Wants Gendry To Make

Game of Thrones season 8 airs Sundays at 9pm ET on HBO.