Image copyright Getty Images Image caption Rob McElhenney's It's Always Sunny in Philadelphia has been commissioned for a 14th series

Rob McElhenney, the actor known for playing Mac in US TV sitcom It's Always Sunny in Philadelphia, has shown off a significant body transformation for the premiere of the show's 13th series.

However, as he explained on his Instagram account, his change has been anything but sunny.

McElhenney, who also created and writes the show, sarcastically suggested "it's not that hard" to achieve his physique.

He posted a split screen of two very different photos of himself, and detailed the efforts it took him to achieve the look.

The regime, which takes "six to seven months", looks like this when broken down, according to McElhenney:

Lift weights six days a week

Stop drinking alcohol

Don't eat anything after 7pm

Don't eat any carbs or sugar at all

Just don't eat anything you like

Get the personal trainer from (Steven Soderbergh's tragi-comic male-stripper movie) Magic Mike

Sleep nine hours a night

Have a studio pay for the whole thing

McElhenney signed off with a sarcastic parting comment about body expectations in Hollywood: "I don't know why everyone's not doing this. It's a super realistic lifestyle and an appropriate body image to compare oneself to."

The post has received 96,000 likes and more than 3,500 comments.

Image copyright Getty Images Image caption It's Always Sunny in Philadelphia will become the joint-longest-running live-action TV sitcom by the end of Series 14

However, McElhenney's appearance has dramatically changed over the course of the show.

He once gained 60 pounds between the sixth and seventh series to poke fun at actors in other shows who continually get better looking.

In the latest episode, McElhenney repeatedly attempts to get other characters to notice his new muscles, serving no story purpose whatsoever.

Other characters shrug off his new appearance and refuse to talk about it, with one saying it looks like McElhenney has put on weight - prompting him to try to cover up.

His fans praised him for going to lengths for "the sake of really dumb jokes".

The show has been renewed for a 14th series which will tie it for the longest-running live-action TV sitcom.

By Paul Harrison, UGC and Social News