On Monday, the rapper, 34, shared a series of sweet photos on Instagram which included personal pics of Aiko's growing baby bump.
"Third trimester already, Life is changing! LottA Gratitude! 🤲🏾🖤🌍✨," Big Sean captioned the collage, which included vintage-style images of Aiko paddling in the ocean wearing a brown bikini and conical hat, with a flower perched behind her left ear.
Aiko is also shown stroking a cat in a red bikini and multi-colored sarong in a video, while other images show the couple cuddling in the surf and Big Sean relaxing in a white shirt and brown leather pants.
In a possible indication of what's the come, one image features a dark blue baby romper bearing the logo of the Detroit Lions. Fittingly for soon-to-be-parents, the gallery ends with the phrase "Pray Big" written on a big wooden sign.
"The couple is overjoyed and looks forward to this next chapter," a representative for Aiko told PEOPLE.
The couple — who have collaborated on a number of music projects together — have been together on and off since 2016.
Renee Rodriguez │ @byreneerodriguez
"As I traveled around and toured, and got to speak to a lot of people and they would share with me their personal stories and share with me how my music has helped them," Aiko said. "And having honest conversations with the people that listen to my music, it's like we're helping each other."
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Reflecting on her own mental health journey, the R&B singer said music was always her way of coping — even before she realized it could be for others too.
"Since the time I could write really, I've been dealing with my emotions through writing. That was always my way of getting through difficult things. Even when I was in elementary school, if I was really angry or really anxious about something, I would write about it," Aiko added.