The twin brother of a man killed in a shark attack has honoured the late surfer, saying they "share the same soul".

Mike Psillakis shared an emotional tribute to his brother Mercury after the 57-year-old was fatally mauled by a shark at Long Reef Beach on Sydney's northern beaches.

"He was my mirror, my blood, my DNA," he wrote in a post on Instagram.

"We share the same soul.

"We had our own language and shared the same dreams."

His brother's energy could be felt in every corner, Mr Psillakis said, as he urged others to hold their loved ones tight.

The 57-year-old was alerting other surfers to the shark before he was attacked, Dee Why local and former pro surfer Toby Martin said.

"Unfortunately, he was the last one furthest out to sea and ultimately paid with his life," he told Nine

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