Soul legend Marvin Gaye's eldest son has added a new twist to the family's legal battle with Blurred Lines hitmakers Robin Thicke and Pharrell Williams by launching his own countersuit against the singers.

Adopted Marvin Gaye Iii has hired his own attorney and has filed a new suit against Thicke and Williams, claiming they committed copyright infringement on four songs.

His legal action, obtained by The Hollywood Reporter, comes on the heels of a countersuit filed by siblings Frankie Christian Gaye and Nona Gaye in October (13), in which they claimed Thicke and his producer pal had illegally sampled two of their late father's hits.

Gaye Iii alleges Thicke's summer anthem Blurred Lines was copied from his father's Got To Give It Up, the singer's Love After War features samples from Gaye's After The Dance, and two other songs, Make U Love Me and Million Dolla Baby, feature his dad's work from I Want You and Trouble Man, respectively.

An attorney for the late soul man's son insists all four Thicke tracks "serve as examples of songs so similar to Gaye's songs as to leave no doubt but that they were each wholly dependent for their very creations upon Thicke's brazen copying."

But while Gaye Iii alleges copying on four songs, he's only bringing copyright claims on Blurred Lines and Love After War.

Thicke, his producer Williams and their collaborator T.I. filed a pre-emptive suit in August (13), asking a Los Angeles judge to declare that Blurred Lines did not infringe on Gaye's 1977 song.

The trio faced similar claims from Bridgeport Music bosses, who own the rights to George Clinton's band Funkadelic's compositions - they alleged the tune bears striking similarities to Funkadelic's track Sexy Ways.

Thicke recently confessed he was eager to reach a settlement to avoid a drawn out court battle with his idol's relatives, but they reportedly rejected a six-figure sum.