It was rumoured that Megan had filmed scenes for the ITVBe show which celebrates its 200th episode on Sunday.
Ex On The Beach and Celebrity Big Brother star Megan joined the cast at their Great Gatsby themed party.
While Megan is friends with some of the cast members, she is best friends with newcomers Chloe Meadows and Courtney Green.
Megan confirmed her appearance at the TOWIE quiz night, hosted by James 'Arg' Argent at The King's Oak in Loughton.
In a Snapchat video, co-star and new love interest Pete Wicks, said: "So guess who's bringing this sort to the 200th episode?"
Grinning, Megan replied: "You'll see me this Sunday on ITVBe at 10pm."
Fans were thrilled with the announcement as they took to Twitter to share their excitement. At the moment, it just appears to be a cameo, but could she become a regular?!
To celebrate the 200th episode, TOWIE producers are bringing fans a feature length show at 10pm, but also a special documentary at 9pm, The Power of TOWIE, hosted by original star of the show Mark Wright.
We're expected to see some familiar faces, old and new, celebrating the reality show which first broadcast in 2010.
Try Reveal's digital edition on iPhone & iPad. Subscribe now & never miss an issue!
Check out some fan reactions to Megan's appearance below:
Omg @Megan_Mckenna_ on towie sunday BUZZING— Emily Carter (@emilycarterxoxo) March 11, 2016
@Megan_Mckenna_ is gonna be on towie on Sunday woo!— AmyEllis (@Horan1993xo) March 11, 2016