A timepiece resonator mechanism including a first support with a first anchor and a second anchor to which is attached a flexural pivot guide mechanism, which defines a virtual pivot axis about which rotatably pivots a pivoting mass, and which includes at least one front RCC flexural pivot and one back RCC flexural pivot mounted in series and head-to-tail relative to each other about said virtual pivot axis, said front RCC flexural pivot including, between said first support and an intermediate rotary support, two straight flexible front blades (110, 210) of the same front length between the clamping points thereof, defining two linear front directions (D1, D2) which intersect at said virtual pivot axis and which define with said virtual pivot axis a front angle (αA), said first and second anchors forming the respective anchors of said two straight flexible front blades (110, 210) farthest from said virtual pivot axis and being both at the same front distance from said virtual pivot axis, and said back RCC flexural pivot including, between said pivoting mass and said intermediate rotary support, which includes a third anchor and a fourth anchor, two straight flexible back blades (310; 410) of the same back length between the clamping points thereof, defining two linear back directions (D3, D4) which intersect at said virtual pivot axis and which define with said virtual pivot axis a back angle (αP), said third and fourth anchors forming the respective anchors of said two straight flexible back blades (310, 410) farthest from said virtual pivot axis and being both at the same back distance from said virtual pivot axis, said flexural pivot guide mechanism being planar, the centre of inertia of the assembly formed by said pivoting mass and any added inertial mass carried by said pivoting mass being on said virtual pivot axis or in the immediate proximity thereof, said front length and said back length being equal to a common length L, said front distance and said back distance being equal to a common distance D, said front angle (αA) and said back angle (αP) being equal to a common angle α expressed in degrees, which satisfies the relationship 107+5/((D/L)-(2/3)) < α < 109.5+5/((D/L)-(2/3)), function of the ratio D/L between said common length L and said common distance D, characterised in that said first support, said pivoting mass, and said flexural pivot guide mechanism form a one-piece assembly. said front RCC flexural pivot including, between said first support and an intermediate rotary support, two straight flexible front blades (110, 210) of the same front length between the clamping points thereof, defining two linear front directions (D1, D2) which intersect at said virtual pivot axis and which define with said virtual pivot axis a front angle (αA), said first and second anchors forming the respective anchors of said two straight flexible front blades (110, 210) farthest from said virtual pivot axis and being both at the same front distance from said virtual pivot axis, and said back RCC flexural pivot including, between said pivoting mass and said intermediate rotary support, which includes a third anchor and a fourth anchor, two straight flexible back blades (310; 410) of the same back length between the clamping points thereof, defining two linear back directions (D3, D4) which intersect at said virtual pivot axis and which define with said virtual pivot axis a back angle (αP), said third and fourth anchors forming the respective anchors of said two straight flexible back blades (310, 410) farthest from said virtual pivot axis and being both at the same back distance from said virtual pivot axis, said flexural pivot guide mechanism being planar, the centre of inertia of the assembly formed by said pivoting mass and any added inertial mass carried by said pivoting mass being on said virtual pivot axis or in the immediate proximity thereof, said front length and said back length being equal to a common length L, said front distance and said back distance being equal to a common distance D, said front angle (αA) and said back angle (αP) being equal to a common angle α expressed in degrees, which satisfies the relationship 107+5/((D/L)-(2/3)) < α < 109.5+5/((D/L)-(2/3)), function of the ratio D/L between said common length L and said common distance D, characterised in that said first support, said pivoting mass, and said flexural pivot guide mechanism form a one-piece assembly.