Justin Theroux makes surprise appearance on Saturday Night Live

Justin Theroux has made a hilarious cameo appearance on Saturday Night Live opposite cast member Kyle Mooney.

The actor, 48, turned up on the show's Leap Day episode to help 35-year-old comedian Kyle get himself in shape.

In the sketch, Beck Bennett, 35, and host John Mulaney, 37, join Kyle - playing themselves - as they try to devise a routine for that week's SNL.

Surprise star: Justin Theroux has made a hilarious cameo appearance on Saturday Night Live opposite cast member Kyle Mooney

Surprise star: Justin Theroux has made a hilarious cameo appearance on Saturday Night Live opposite cast member Kyle Mooney

But after being left out of a proposed sketch about male strippers, because he is always typecast as the 'dork', Kyle decides to get buff.

With the help of guest star Justin and a nutritionist, the comedian sets up a personal gym in his office, and becomes more 'attractive' to his co-workers by piling on muscle.

Kyle showed up two days later with bulging biceps and a chiseled chin after putting on 37lbs of muscle — in two days — so that he could star in a male strip club sketch John was writing.

Feel the burn: The actor, 48, turned up on the show's Leap Day episode to help the 35-year-old comedian Kyle get himself in shape

Feel the burn: The actor, 48, turned up on the show's Leap Day episode to help the 35-year-old comedian Kyle get himself in shape

But after extensive rewrites, John only wants dorks in the sketch and so beefcake Kyle is cut again, and then fired from SNL for good measure.

The long-running sketch show saw former writer John Mulaney return as host for a third year in a row, and was joined by Jake Gyllenhaal, 39, to provide some star power.

Mulaney played to his strengths in the monologue with a hilarious stand-up set featuring tangents about how terrible men are at making friends and the idiosyncrasies of the Bill of Rights.

Hilarious: After being left out of a proposed sketch about male strippers, because he is always typecast as the 'dork', Kyle decides to get buff with the help of 'trainer' Just Theroux

Hilarious: After being left out of a proposed sketch about male strippers, because he is always typecast as the 'dork', Kyle decides to get buff with the help of 'trainer' Just Theroux

Awkward: But after extensive rewrites, John only wants dorks in the sketch and so beefcake Kyle is cut again, and then fired from SNL for good measure

Awkward: But after extensive rewrites, John only

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