The nine-year-old had her eyes closed as she cuddled up to her soon-to-be sister-in-law, while Nicola wrapped her arms around Harper from behind.
"Missing the gorgeous and sweet Harper Seven extra today," the American actress, 25, captioned the photo. It appeared to have been taken at the Beckhams' family home in the Cotswolds, with a huge lawn and plush cream garden sofas visible in the background.
WATCH: Inside Harper, Brooklyn and Nicola's sweet shopping trip
The reflection in Nicola's sunglasses, meanwhile, provided a glimpse of the outdoor swimming pool which Brooklyn's brother Romeo unveiled for the first time in July.
Brooklyn, who took the photo, was among the first to comment on his fiancée's post, writing: "Love you guys." Nicola's followers also flocked to the comments section to share their thoughts, with one remarking: "How cute Nicole! You have your Mini-Me with you for the day!"
Nicola and Harper cuddled up together in a sweet new photo
A second added: "If only my boyfriend’s siblings liked me like this," while a third wrote: "Aww how sweet."
Nicola has been spending plenty of time with Brooklyn's family over the past few months, from attending Brooklyn's 21st birthday back in March to visiting Victoria Beckham's London store for a shopping trip in July. So it's no surprise that being apart would come as a shock for both of them!
Nicola spends lots of time with Brooklyn's family
Former Spice Girl Victoria even enlisted Nicola's help to capture a fabulous holiday snap of herself with Harper. The pair were posing in a hammock with their legs up in the air at what seems to be their holiday villa, complete with majestic white columns in the background.
In the snap, Harper wore a lovely gingham dress and a fresh pair of white Converse on her feet, while mum Victoria donned a sleek pair of heels.