In the snap, baby Ella can be seen peacefully sleeping, and looks ever so cute with a full head of hair, while wearing a pink all-in-one suit.
Captioning the photo, Dan said: "Our beautiful little girl."
Jacqueline followed Dan's photo with one of her own as she declared her love for her new family.
She gushed: "Such a lovely day, feeling so lucky right now. I'm so in love with my @DannyO and my beautiful baby girl Ella Selina Osborne. Perfection."
Commenting on Instagram, Jacqueline added: "My first Mother's Day and Ella is now a month old."
Earlier in the day, Dan praised EastEnders actress Jacqueline, who gave birth to Ella on 15 February.
Dan said: "Happy first Mothers Day to my beautiful @jacquelineMjos... The best mum Ella could ever wish for! We love you more than anything."
Just last week, Dan gushed over Jacqueline, saying she makes him "the happiest man alive".
Since the birth of their baby girl, Dan has etched Ella's name across his ribcage, under the name of his son Teddy, and he also got the letter 'J' tattooed on his wrist in honour of Jacqueline.
Ella is Jacqueline's first child. Dan is already dad to son Teddy from his previous relationship with ex-girlfriend Megan.
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All you need to know about Dan and Jacqueline!