The girls were joined by their co-stars Dan Osborne and Tom Pearce at the event on Thursday night (18 September).
While Lydia looked pretty in white, Ferne beamed in a coral frock as they promoted the hit Essex-based reality show.
Lydia took inspiration from Sister Sledge's hit song, 'We Are Family', as she posted a group photo. She said: "We are family. I got all my sisters and brothers with me."
The girls also mingled with Loose Women's celebrity panelist Jamelia, I'm A Celebrity... Get Me Out Of Here! star Joe Swash and Take Me Out host Paddy McGuinness.
After the event, Ferne and Lydia attended the after party, where they enjoyed music from the likes of Britain's Got Talent stars Lucy Kay and Collabro.
The cast of The Only Way Is Essex are heading to Ibiza this weekend where they'll begin filming opening episodes for the new series.
The 13th series of TOWIE will no longer air on ITV2, as new channel ITVBe will be its exclusive home when the reality show returns next month.
Upfronts is an annual event hosted by ITV aimed at advertisers and media buyers to promote the channel's latest content, extensive programmes and new commissions for 2015.
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ITVBe promo video: