Janet Jackson and her estranged husband were together again this week ... in a courtroom to begin divorce proceedings.

Janet and Wissam Al Mana were spotted leaving the Royal Courts of Justice in London Thursday afternoon after the apparent first round of their divorce battle wrapped up. The singer left with her assistant and legal team while her Qatari multi-millionaire ex flew solo.

As you recall ... Janet married Wissam in 2012 and they had a son together named Eissa in January. They split just a few months later.