Family, friends and colleagues paid tribute to Sapper Richard Walker: a "devoted father", who was killed by an Afghan soldier on Monday.
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He has agreed a two-year contract at St. James' Park and becomes the tenth new face in the Magpies' first team squad this summer.
On the back of three consecutive Championship wins, the Magpies sit fourth, poised to move into the automatic promotion places.
Callum Young, who will now be 23, was last seen on August 27 last year at his home in Hylton Road.