The 29-year-old attacker has left Forest to re-sign for his former club and Championship rivals QPR, where he is very popular.
The Scotsman has signed a two-year contract with London outfit Rangers, with the option of a third year.
Mackie joined the Reds from QPR in the summer of 2013, but he failed to make a huge impact at the City Ground.
The attacker could score just four goals and managed to create only 32 chances in 45 Championship appearances in the 2013-14 season.
The 29-year-old had a pass accuracy of 75% and a shot accuracy of 55%, and won 28 headers, 37 dribbles and 54 tackles.
The former Plymouth Argyle man was sent out on loan to Championship rivals Reading for the 2014-15 campaign.
Mackie scored five goals and created 24 chances in 32 league appearances for the Royals this past term.
The former Milton Keynes Dons attacker had a pass accuracy of 74% and a shot accuracy of 50%, and won 30 headers, 27 dribbles and 24 tackles.
Following Mackie’s transfer, supporters of QPR and Forest took to Twitter to have their say.
Below are the best reactions:
Queens Park Rangers fans:
Hands down one of the most passionate players we've had, clearly loves the club. Scored some vital goals too! Great news #ReturnOfTheMack— Soph. (@sophqpr) June 16, 2015
Nottingham Forest fans:
@Official_NFFC Decent solid 6-7/10 performer, but no choice when on those wages but to get him off the bill.— Jack Grummitt (@Jack_Grummitt) June 16, 2015
@official_nffc shame really cos mackies not bad but these ffp rules are! Makes sense i suppose?— christopher england (@England8050) June 16, 2015