Marine Mackin also has a brother serving in Afghanistan
A Royal Marine killed in southern Afghanistan on Sunday has been named as Travis Mackin, aged 22, from Plymouth.
Marine Mackin, who died in an explosion while on patrol in Kajaki, was described by the MoD as "incredibly popular and exceptionally loyal".
At the time he was leading his team in an operation between Victor Company, 45 Commando Group, and Afghan troops.
He was the 139th member of British forces to die since the start of operations in October 2001.
The MoD said Marine Mackin was a member of the specialist team mentoring the Afghan National Army and the Afghan National Police in Kajaki.
It said his family had strong links with the military and one of his brothers, Corbin, was serving with the 1st Battalion The Rifles, in Helmand.
"The loss of such an incredibly popular and exceptionally loyal member of our band of brothers is a tragedy," it added.
In a statement, Marine Mackin's family said: "Travis was a much loved son and brother who is never going to leave us and will be in our hearts and souls forever.
"He lived for the Marines and was so proud of his uniform. His untimely death leaves a massive hole in all the lives of his family and friends.
"He touched the hearts of all those that met him and we are so proud and honoured to have had him in our lives."
Marine Mackin's girlfriend Laura said he was "irreplaceable".
"To me he was the most honourable, unselfish and caring person I have ever known and he never ceased to make me laugh," she added.
"I will miss him beyond words but equally I am so proud to have known this wonderful man."
Col Haydn White, Commanding Officer 539 Assault Squadron and the Armoured Support Group Royal Marines, described Marine Mackin as a "highly professional soldier with an infectious sense of humour".
"Wherever he served, Travis was guaranteed to provide his best and was an accomplished soldier and signaller.
"He always had a real zest for life and those that met him were better for the experience."
Defence Secretary John Hutton paid tribute to Marine Mackin.
"I have heard that Marine Travis Mackin was an extraordinarily committed and confident marine who led from the front, " he said.
"His loss will be a devastating blow for his family, friends and colleagues. My thoughts are with them, and his brother Rifleman Corbin Mackin, at this the most difficult of times."