Sir Paul McCartney -- Here Comes the Sun ... And Lots of SPF!

Paul McCartney got a little help from his friend/wife while roasting in the sun.

Paul and Nancy Shevell have been chilling in Ibiza ... where most people are capable of applying sunscreen on their chests without assistance -- but most people aren't Beatles and Knights.

Sure ... 53-year-old Nancy might look kinda like a nursemaid lathering ointment on a patient -- but we're guessing rubbed up 72-year-old Paul ain't complainin'.