Liam Scales has joined Aberdeen on a season-long loan from Celtic and Anthony Stewart has agreed to join the Dons next month.
Republic of Ireland Under-21 cap Scales, 23, moved to Celtic from Shamrock Rovers last summer and made 13 appearances, scoring twice.
Fellow defender Stewart, 29, will join on a two-year deal after rejecting a new contract at Wycombe.
On Monday, the Dons signed right-back Jayden Richardson, 21.
Richardson, who has signed a three-year deal, arrived from Nottingham Forest for an undisclosed fee and played 23 times on loan at Notts County last term.
Manager Jim Goodwin has now added four players to his squad for next season with Albania midfielder Ylber Ramadani agreeing his move from MTK Budapest earlier this month.
On Sunday, right-back Calvin Ramsay left Aberdeen to join Liverpool for an initial £4.2m.
Goodwin says Scales is "a strong character with a winning mentality" and described the experienced Stewart as "a proper, old-fashioned centre-back that enjoys the art of defending".
And Goodwin said of Richardson: "He is a very quick, dynamic and attacking full-back who, I am sure, will use this as a platform to go and prove himself."
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