The former Spice Girl accompanied her Formula 1 team boss beau to the Zoom Formula 1 Charity Gala in London on Friday, 16 January.
Geri and Christian became engaged in November 2014, choosing to discreetly share their happy news via an announcement in The Times newspaper rather than a press release.
Their brief message said: "The engagement is announced between Christian, son of Mr and Mrs G M Horner and Geraldine, daughter of the late Mr L F Halliwell and Mrs A Parkinson."
It's believed they've been dating since March 2014.
As well as planning a wedding, singer Geri is also working on new music. She's been sharing photos of herself in the studio with fans via Twitter.
On 15 January, she revealed she'd "just written a beautiful song" and was "proud" of its lyrics.
Meanwhile, fiancé Christian has told The Mirror Geri is so devoted to her music she even records tracks in their bathroom!
Geri is constantly writing down ideas and melodies for new songs. She even records vocals on the toilet because the bathroom has good acoustics. She's certainly dedicated to her art."
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