For the occasion, Middleton donned a Orla Kiely pale pink long-sleeve dress with black detailing and black pumps that subtly hugged her growing baby bump. Watch footage of the moment here (our hearts are totally melting):
The royal trio gathered on the platform along with the cast of Paddington 2 for the Charities Forum event, which brought 130 children from various charities for a ride on the Belmond British Pullman train.
It's a nice change to see Middleton out and smiling in light of her battle with hyperemesis gravidarum, a form of severe morning sickness.
She has had to miss several occasions (including her son Prince George's first day of school) because of the severity of the sickness, but it thankfully didn't look to be bothering her too much on Monday.
A version of this article originally appeared on InStyle U.S.