The Duchess of Cambridge’s younger brother made the post on Sunday after rumours about the relationship progression began to swirl.
“She said OUI,” the 32-year-old wrote on Instagram.
“Our secret is out but we couldn’t be happier to share the news.”
In the snap, the happy couple are pictured atop a hill in England’s Lake District, the same region where Pippa Middleton’s now-husband James Matthews proposed to her in 2016.
The entrepreneur’s Instagram stories were just as loved up, and showed a moving montage of shots through the couple’s relationship, which began last year.
“I asked @alizeethevenet a question the other day,” James explained.
The couple’s happy news was first revealed by Daily Mail reporter Richard Eden on Saturday after he spoke with one of James and Alizee’s friends.
“I can reveal that James is to wed his French girlfriend, Alizee Thevenet,” Richard wrote, adding that the bride-to-be has been spotted wearing a “beautiful sapphire sparkler”.
James first gave royal watchers a glimpse into his ultra-private personal life when he quietly made his Instagram public earlier this year.
Since then, the handsome entrepreneur has treated us to adorable pics of his beloved pooches - Ella, Zulu, Inka, Luna and Mabel - but not much else.
He surprised everyone in July by including someone extra-special in his latest post: his new girlfriend Alizee.
Alizee, a French financial analyst, is pictured laughing in a red bikini as the self-professed “dog dad’s” golden retriever Mabel leaps into a swimming pool.
A clearly smitten James - who broke up with his girlfriend of five years, Donna Air, in early 2018 - included the caption, “caption this.”
The blonde beauty first popped up in James’ page back in May, and it looks like things have been getting pretty serious since then.
The couple has reportedly been dating for a year, meeting in London mid last year, according to Mail Online.
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