Demi can werk!!
[Image via WENN.]
The Kate Middleton wasn't the only Duchess celebrating St. Patrick this weekend.
Fergie came out on Saturday night to celebrate the Irish holiday and the launch of her personal trainer Don "DB" Brooks's Don-A-Matrix Training.
And in case you're wondering who the girl in black is, it's Fergie's sister Dana Ferguson.
[Image via Daniel Tanner/WENN.]