You just don't know what you can get from those 'It's Always Sunny in Philadelphia' folks. The show, which is in its thirteenth season, continues to go from strength to strength. Its season finale aired in the states last night and proved it's also not afraid to shift tone from time to time and pull it off with aplomb.

 

Fans of the show will know that Mac (Rob McElhenney) finally came out back in season 11, however in the finale last night entitled 'Mac Finds His Pride', he admits to Frank (Danny DeVito) that he is still struggling to come to terms with his sexuality telling him: "I don’t know where I fit in as a gay man and it’s starting to get to me. I’m not feeling very proud."

Frank, who is trying to get Mac to take part in the gang's pride parade float tells him: "I never really got you and, to be honest, now that you’re gay I get you even less. Nothing against it, I just don’t get it."

Despite this, Frank still supports Mac fully when he decides to come out to his imprisoned father with what unexpectedly turns out to be a five-minute jaw-dropping contemporary-dance number with professional ballerina Kylie Shea.

Although Mac's dad walks off mid-performance, the rest of the inmates and Frank are moved to a standing ovation afterwards, with Frank declaring through tears: "Oh my God, I get it. I get it."

Seriously, we know this doesn't sound like an episode of 'It's Always Sunny in Philadelphia' at all but they well and truly pull this off.

Prepare to be blown away by Mac's dancing:

McElhenney, who also created 'It's Always Sunny' and writes it along with co-stars Glen Howerton and Charlie Day, said of the performance: "We got a really overwhelming emotional response from the LGBTQ community last year. I took it seriously and I felt it would be completely unexpected to have this much more emotionally resonant end to the season, he told Vulture.

"You would expect that Mac would express himself through the art of contemporary dance and it go horribly wrong, until you realize that’s not the direction we’re taking."

The end of the episode also revealed that the dance routine was the reason Mac had got into such great shape, which had been a running joke in the show as the gang refused to acknowledge Mac's new body, despite him flaunting it at every occasion. (McElhenny also previously gained 50 pounds to become "Fat Mac" in the seventh season of 'It's Always Sunny'.)

McElhenney's commitment to this final dance is also beyond impressive, having zero experience prior to this. He called on celebrity trainer Arin Babaian who has worked with Channing Tatum and Joseph Gordon Levitt, to get him into shape.

"I worked with Arin to get into good enough cardio shape to be able to dance for two hours a day and we did a lot of lifting and also a lot of stretching," McElhenney said. "I’m not a very limber person, so I stretched for like an hour a day just to be able to move my body in those ways which I was never able to do before and will never be able to do again."

While he also recruited choreographer Alison Faulk , who had previously worked with Channing Tatum on 'Magic Mike'.

“Rob came out of the writers room saying he wanted it to represent the struggle, the push and pull, and that helped Leo and me to put the choreography together in a way that showed vulnerability and strength,” Faulk said.

"We thought what would be funny about it is that it’s kind of confusing, " Rob said. "We’ve set it up in the script that his explanation is also intensely confusing.

"We realized if he couldn’t really verbalize what it is that’s happening to him, it doesn’t matter because he’s just hoping for someone — whether it’s God, his mom, or his dad, or his surrogate father Frank — to say that it’s all right to feel what I feel and be who I am."

Danny DeVito said of the performance: "It’s just remarkable how little command Mac has of his intelligence.

"He’s the most conflicted person I’ve ever met in my life. I thought it was brave thing for Rob to do this, to tackle this story in this way. I was very proud that he tackled the insides of Mac and I was very moved by the dance. Thank God for the woman, because she was brilliant! I could watch it all day long. I thought it was really, really sweet, man."

Excuse us while we go watch it again.