Serena Williams and daughters. Photo: Serena Williams/Instagram; Stefanie Keenan/VF24/WireImage

Serena Williams agrees that two is always better than one.

On Thursday, Aug. 15, the retired tennis pro, 42, shared her admiration for her daughters Adira, 12 months, and Olympia, 6, whom she shares with husband Alexis Ohanian, as her youngest turned one. The proud mom of two posted a few throwback snaps on Instagram of herself with Olympia from her maternity shoot before welcoming Adira.

The mother-daughter duo can be seen smiling in a bed of flowers wearing matching pink flowy dresses. “Olympia is always there for me,” Williams said in her caption. “Before having a second child, I always wondered, ‘how could I love anything as much as I love @olympiaohanian?'”

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She continued, “Then Adira came along … she is so special, so fun, so funny, so loving, so sweet and so strong!!! You see, God makes your heart get bigger. Because my love for Olympia has not dimmed. My heart simply now is doubled the size and I have a greater capacity to love more!”

Earlier in the day, Williams shared a few more sweet pictures from her previous photoshoot in honor of her little one’s first year.

In her first celebratory post, the mother of two wrote, “A year ago today – August 15th – I gave birth to my second baby girl, Adira River Ohanian. She is a true light. Here’s a peek inside my maternity shoot. @adiraohanian.”

In her second post, Williams posed with daughter Olympia and husband Ohanian, with Olympia kissing her mom’s stomach. She also shared a photo of her side profile, putting her two hands on top of and below her bump.

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“Adira is a girl’s name of Hebrew origin and means ‘mighty,’ ‘strong,’ and ‘majestic.’ The elegant name is popular in many cultures around the world,” Williams shared in her second post. “Adira is the feminine form of the classic name Adir. It is a Biblical name, meaning ‘Strong One.’ @alexisohanian @olympiaohanian.”

Speaking to PEOPLE in May, Ohanian shared that he’s excited to see his younger daughter start to get her footing, noting it’s “fun because she’s getting more mobile.”

“She’s able to have a lot more fun with her sister in terms of playing. You can already see the interactions between them. It’s a big age gap, and Olympia has a little bit of that maternal spirit. She’s like, ‘This is my baby,’ and it’s great to see them together,” Ohanian shared.