Robin Thicke and Pharrell Williams spent time in a Los Angeles courtroom Tuesday, as the trial started in their copyright dispute with Marvin Gaye's children over the mega hit "Blurred Lines."

RadarOnline reports the recording artists are embroiled in a multimillion dollar legal dispute with Gaye's relatives over how much of the late Motown singer's 1977 hit "Got to Give It Up" to compose "Blurred Lines."

Janis Gaye, the late singer's wife and mother of his children, was the first witness to take the stand. She helps the Gaye estate regarding the copyrights to her late husband's songs. She testified that she initially thought "Blurred Lines" was great and brought new life to "Got to Give It Up," but later she realized the song's creators had not licensed the rights to Gaye's song, reports ABC News.

"The evidence will show 'Got to Give It Up' was used as a blueprint for 'Blurred Lines,'" Richard Busch, lawyer for the Gaye family, told jurors.

He added that the two songs having so much in common was "not random."

Attorney Howard King, who is representing Thicke, Williams and T.I. (his real name being Clifford Harris, Jr.), said the Gaye family's claim that the song earned $40 million is way off-base, and that "no one owns a genre or a groove," making their claims invalid. King said the musical trio "didn't copy Marvin Gaye," but rather "created the song as they have for the other hundreds of songs they've written." He added that neither Thicke nor Williams have ever been sued for copyright infringement previously.

The trio's camp maintains that the song's writing credits are 65 percent Williams', 22 percent Thicke's and T.I. accounts for 13 percent.

The legal disputed began in August 2013 when Thicke, Williams and T.I. filed a preemptive lawsuit over "Blurred Lines" after Gaye's estate and Bridgeport music reportedly threatened legal action because the song is too similar to Gaye's "Got to Give It Up" (and Funkadelic's "Sexy Ways"). The Thick-Williams-T.I. lawsuit accuses the Gaye estate of making an invalid copyright claim since expressions -- not individual ideas -- can be protected.

Williams maintains that the two songs are "completely different."

In October, a judge sided with the Gaye family, ruling that their experts provided enough evidence for the case to go to trial.

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