Ed Sheeran plays his guitar and sings "Thinking Out Loud" during a copyright trial

In an effort to show how common the four-chord progression for his hit song "Thinking Out Loud" was, Ed Sheeran picked up his guitar and played a mash-up of his songs and Marvin Gaye's.

The mini-concert took place on Monday while Sheeran was still testifying in his copyright infringement case.

The family of "Let's Get It On" song co-writer Ed Townsend has accused Sheeran of stealing the song's music sheet.

"Did you copy anything from 'Let's Get It On' when you wrote 'Thinking Out Loud?'" defense attorney Ilene Farkas asked.

"No," Sheeran replied.

"Were you thinking about 'Let's Get it On?'" Farkas asked.

"No," Sheeran answered.

Because of the resemblances and inspiration Sheeran claimed the Northern Irish singer provided, he claimed his producers started referring to "Thinking Out Loud" as Sheeran's Van Morrison song.

On Thursday, the most recent trial day, Sheeran discussed the writing process of "Thinking Out Loud" and played a portion of the song. He testified that he overheard singer-songwriter Amy Wadge playing some chords from another room and telling her they needed to use it for a song in February 2014, which is when the song was co-written by her.

The music of either man has been the subject of copyright disputes before. Sheeran won a copyright infringement case involving "Shape of You" last year, while Marvin Gaye's heirs, who are not parties to this current lawsuit, won a case involving "Got to Give it Up" against Robin Thicke and Pharrell Williams in 2015.