Whitney Houston added two new songs to her set during her concert Wednesday in Adelaide, Australia. Halfway through the show, during the “unplugged” portion when Houston, 46, performs old hits, she announced it was her daughter Bobbi Kristina’s 17th birthday, a source close to the singer told PEOPLE. Houston then sang “Who Would Imagine a King” from The Preacher’s Wife. “[It's] one of Krissy’s favorites,” the source says, “and is not in the show.”

Then a birthday cake was rolled out on stage, and Houston invited her daughter to come up, joined by her dancers and another tune – “Happy Birthday,” which was sung by the entire audience.

Mother and daughter also celebrated the occasion in Sydney earlier in the week during a stop on the singer’s Nothing But Love world tour.

“They rented a beautiful boat and took a four-hour cruise all around Sydney Harbor with Krissy’s friends, the dancers and family members,” adds the source. “That was the pre-birthday celebration. The cake at the concert was a complete surprise to Krissy. She had no idea!”

I love that Bobbi Kris travels with Whitney Houston and I’m happy to see the love displayed between the two of them. It’s soooooo cute!