The 38-year-old singer's father had asked him if he would provide the entertainment at the ceremony and Williams was thrilled with the gesture, reported the Sun online.
"Robbie is thrilled - he is Best Man and will sing. There's talk he will do the first dance, maybe something during the ceremony too," a source said.
Three years ago club singer Pete performed at Williams' wedding with Ayda Field in Los Angeles.
The 64-year-old patriarch had then said that he was hopeful his son would perform at their nuptials too.
"The next thing is to plan the marriage. When it happens Robbie might sing, wouldn't that be lovely. We've got to all get together and plan it."
Pete divorced Williams' mother Janet when the singer was only three-year-old.
