Milne will not be available for selection until the clash against Somerset on June 28.
Across three previous spells with Spitfires the 29-year-old claimed 38 wickets in 28 Blast games at an average of 19.10.
“I love being a Spitfire and I’m really excited that the opportunity has arisen for me to come back to Kent for a fourth time," said Milne, who has a T20 career economy rate of 7.72.
“It’ll be great to see familiar faces in the dressing room but I’m also looking forward to working with the new talent that has joined since my last stint in 2019."
Director of cricket, Paul Downton added: “We’re delighted that Adam will be coming back to be a Kent Spitfire once more.
"He is a world-class T20 bowler who has made a significant difference to our side every time he has played for the Spitfires. I am sure our members and supporters will be excited to welcome him back for the later stages of the Vitality Blast."
The right-arm fast-bowler joins Afghanistan's Qais Ahmad as Kent's second overseas player for the Blast.
Having undergone a mandatory quarantine period in the third-party country, Ahmad will be available for selection from Kent's third game of the group phase, against Gloucestershireon June 13.
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