Erin Foster is engaged to her partner Simon Tikhhman

Erin’s older sister Sara Foster broke the news on her Instagram account when she uploaded a picture of the ‘Barely Famous’ actress showing off her engagement ring.

And Sara, 38, joked in the caption: “Ladies, i guess the moral of the story is stay crazy because apparently it gets you a ring (sic)”

Moments later, Erin took to her own Instagram account to post a photo of her shocked reaction, and wrote: “How on earth did I pull this off?”

The ‘Circle’ star began dating the businessman in August last year, when sources said Simon treated the actress “wonderfully”.

Insiders said at the time: “It has been around six months and they are very serious. Erin and Simon met through mutual friends in L.A. Things are going well. Simon is a really good guy and treats Erin wonderfully.”

Meanwhile, the engagement comes just two months after Erin’s dad David, 69, tied the knot with his 35-year-old partner Katharine McPhee in London in June.

Erin and Sara previously praised Katharine prior to the wedding, and said they were “lucky” to have a new stepmother they are “genuine friends” with.

Sara said: "We love our future stepmom. Our dad's very happy and we're excited."

To which Erin added: "We got very lucky that she is so funny and we genuinely are friends with her. [You have to] have a sense of humour to be in this family.”

David has Erin, Sara, and 32-year-old daughter Jordan with his ex-wife Rebecca Dyer, as well as 46-year-old daughter Amy from his marriage to B.J. Cook, and 49-year-old Allison, whom he placed up for adoption when she was born but reconnected with almost two decades ago.