The Rhythm Nation hitmaker celebrated her special day on 16 May and believed she would be enjoying a sushi meal with her billionaire husband, only to find that he had organised a surprise party at the Hyde Lounge in Los Angeles.
According to Us Weekly, the singer's older brother Jermaine Jackson, 60, was among the 30 guests in attendance at the private bash.
A source told the magazine: "Thirty of her closest friends and family were there." The insider claims that Jackson had "two beautiful cakes" and partied with her group until 1:30am.
Sharing further details of the top secret shindig, another insider told E! News: "When she arrived in the venue with her husband and bodyguard, they escorted her to the patio where her closest friends and some family members were waiting for her with a big surprise!"
The couple's united front comes just days after it was alleged that Jackson's marriage to the 39-year-old businessman is on the rocks.
A friend of the couple's reportedly told E!: "All the bliss that Janet experienced pre-marriage with Wissam and in the first couple of months is gone."
However, another source shut down these allegations, telling the publication: "From what I was told, she never said divorce. From what I'm told, she's staying with him."
Entertainment Tonight also insisted the couple's marriage was stable with a source telling the website: "The rumours about their marriage are a lie. They are very happy and very much together. In fact, the couple has recently purchased an even larger home in New York."
The pair married in a top secret ceremony in 2012 but the Grammy-winner only confirmed the news on her website.
Part of the statement read: "The rumors regarding an extravagant wedding are simply not true. Last year we were married in a quiet, private and beautiful ceremony."
The That's The Way Love Goes singer will be returning to the spotlight later this year with a brand new tour and album.