In theory you could have up to 9 Queens on the board at once. You start with one, and each pawn can promote to one. In practice this is very unlikely as your opponent would be wise to resign the game well before getting that far.
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You don't 'get your queen back'. Promotion is the gaining of a completely new piece. You have eight pawns and can promote every single one to queen if you ever got the chance. You could have nine queens, if you can somehow avoid checkmating the king by bunching them in one corner.
You can have up to 10 queens (9 pawns promoted to queen + 1 original queen). Very rare does this happen.
Theoretically, you could have nine queens, if you managed to promote every pawn. This could not possibly happen during a real chess game.