The actress, 44, who announced she had welcomed her third child in May, shared a sweet post on Instagram to mark the occasion - and fans can't get over their likeness.
Sienna Miller looked stunning in a simple white summer dress as she stepped out in West London on Thursday night for the Debute pop up shop opening party.
The couple have been documenting their quest to purchase a holiday home where they can 'make memories' with their two children Abel, four, and Sienna, 10 months.
The actress, who recently gave birth to her third child, is set to tie the knot with actor Oli Green, after taking the next step in their relationship.