The News understands the left-back is on the verge of leaving Pompey for their League One rivals.
Brown has been having a medical with the Londoners, and is expected to go straight into Mark Robinson’s team for their home clash with Shrewsbury on Saturday.
The 31-year-old was told he could go by Pompey in the wake of Denver Hume’s arrival from Sunderland, with six months remaining on his existing deal.
Blues chief executive Andy Cullen today told The News there has been no official contact with the Dons, over the man who’s made 130 appearances since arriving from Bristol Rovers in 2018.
That situation has accelerated, however, with Wimbledon making their move in the face of competition from a number of League One clubs.
The Dons have money to spend following the sale of Ollie Palmer to Wrexham for £300,000, allowing them to finance a move for Brown.
And it’s a switch which suits the former QPR trainee, who lives near the capital and has business interests in that area.
The Blues vice-captain, of course, caught the eye against Wimbledon at the end of last season as he bagged two goals in Pompey’s 3-1 success on the penultimate weekend of the campaign.
His departure frees up further space in Cowley’s wage bill as he bids to complete his own squad reshaping ahead of Monday’s transfer deadline.
Cowley has brought in four players - Hayden Carter, Tyler Walker, Ollie Webber and Denver Hume.
Brown will become the seventh player to depart this month, with Ellis Harrison, Paul Downing and John Marquis joined by the exits of loanees Miguel Azeez and Gassan Ahadme. Alex Bass has joined League Two Bradford on loan.
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