The left-back and sometime Pompey skipper sealed a move to AFC Wimbledon on Friday following 131 appearances and six goals.
Brown admits the £200,000 arrival of Denver Hume represented the ‘writing on the wall’ for his first-team ambition during the remainder of the season.
Crucially, the long-serving 31-year-old was also out of contract at this season’s end.
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Nonetheless, he insists he first discovered there would be no fresh Blues deal in a phone call from Danny Cowley on Monday evening – when he was told he could leave.
By the end of the week, Brown had joined Wimbledon in a two-and-a-half-year agreement.
He told The News: ‘It came about on Monday night when I was sitting down having food with my family.
‘Danny Cowley rang and told me they had signed Denver Hume. He’s brought him in to play – I ain't going to play, I won’t be getting a contract in the summer and will be free to leave.
‘That was the first time he had mentioned my contract.
‘I had a bit of interest in the summer and the conversations then were “There’s no way I want to lose you, if I’m here you will 100 per cent be here, you are so important to the squad and changing room”.
‘They were probably the same conversations I was having throughout the course of the year – until Monday.
‘I would have liked to remain until the end of the season, I think I could have offered a lot in the back four, I know I can.
‘You’re not stupid, you are not silly, you know if they bring someone then it’s not looking great for me. I had seen Denver Hume mentioned in the press and knew the writing was probably on the wall.
‘I had worked it out for myself, but there are ways to do it – probably not over a phone after you’ve been somewhere three-and-a-half years and served as vice captain.
‘It is what it is, it’s the 21st Century now, I don't expect too much of people anywhere across the whole of life, you can’t be shocked by things.
‘It’s not me moaning, I respect him (Cowley) for being honest and it has actually worked out for me. I am 15 minutes from home, having joined a fantastic football club in Wimbledon.
‘Would I have handled it differently? Yes. But it’s not a perfect world, is it.’
Having been informed he was surplus to requirements on Monday evening, Brown himself was surprised at the subsequent level of interest.
By Thursday, the defender had been informed of up to five League One clubs keen to recruit his services – yet his preference lay with Plough Lane.
Brown added: ‘As soon as someone says you can leave, the feelers go out and you wait to see what happens. I surprised myself with the amount of interest.
‘It’s always nice when someone doesn’t want you, but another four or five in League One do.
‘I found out on Monday and by Tuesday we had three clubs interested, by Wednesday it was 4-5 – it happened within 24 hours.
‘I was training with Pompey’s squad on Thursday. By the afternoon it had basically been done with Wimbledon.
‘It’s a nice feeling, when someone says you are not good enough for them – and then 4-5 people at really good clubs are saying “Well, I’ll take you”.
A message from the Editor, Mark Waldron