Martin is also retiring as Unitedâ€™s chief scout later this year, leading some to suggest a brotherly pact may have been agreed.
Martin told his brother he reckoned the announcement came out of sibling rivalry.
He joked: â€śI told him I knew what he was up to, trying to steal my thunder ahead of my retirement.
â€śI told him that I had all the press and television lined up for me making my own announcement but now heâ€™s gone and spoiled it.
â€śHe burst out laughing, of course. We didnâ€™t make any pact and we didnâ€™t discuss it at all.
â€śIt just seems that the time was right for both of us. For Godâ€™s sakes, weâ€™re both old enough. I hope we manage to see more of each other and the families spend more time together because he is a great family man and he looks after his family extremely well.â€ť
He added: â€śHe absolutely dotes on his grandchildren and I think having more time with them is something that he will appreciate.â€ť