The British rock band made the announcement on Thursday, confirming the sad news.
They tweeted: “#JackSonni Rest In Peace #DireStraits”.
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“Our beloved Jack has left a void in our heart and soul,” a statement on Facebook on the Dire Straits Legacy account reads.
“We will miss you so much. You are forever with us.”
Sonni, who hails from Pennsylvania in the U.S., is best known for being “the other guitarist” in Dire Straits, joining the band for 1985 hit album and tour Brothers In Arms.
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Dire Straits Legacy, a band Sonni performed with, said he had to pull out of gigs earlier this week due to undisclosed ‘health problems’.
“Dear fans, unfortunately, Jack Sonni will not be able to participate in our next gigs because of health problems,” the post read.
“Jack get better soon, we are waiting for you! With love, the DSL family.”
Sonni was American and was asked to join the British rock band Dire Straits in 1984.
They are known for hits including Walk of Life, Brothers in Arms and You and Your Friend.