My son created a song, published it on YouTube years ago and maybe 3 years later after he published it a well known musician used the music/beats

About 10 years ago my son went to a recording studio and created a song, after the song was finished, he then made a video & published it on YouTube in the mid to teen 2000's & about 2-4 years later a well known musician used the same beat/music/melody that he(my son) used in his publicised video to create a song of his own. My son has explained to me that he didn't create the music himself & someone else was responsible for that,however, my son was responsible for releasing the music that he made with this beat/music/melody & once I informed him about the similarities of his work & the well known musicians song he asked for my assistance with this matter. Does my son & the original producer that he worked w/have grounds for a lawsuit based on the fact that the music was not only published years before this artist came out w/his song because it is the same tune that my son used prior to the artist usage of said music? If so what are the steps to rectify this situation? How can I help?