The star, who joined Petty and his band for dates in North America in 2008 and 2009, joined the headliners for renditions of his songs "Can't Find My Way Home" and "Gimme Some Lovin'."
The London shows are Petty's first in the U.K. since he performed at a tribute to late pal George Harrison in 2002.
Tom Petty & the Heartbreakers are scheduled to headline the rain-soaked Isle Of Wight festival on Friday before embarking on a mainland Europe tour.
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