When animating the frame of an NSImageView, the image resizes instantly - how can I make that animated, too?

Question

I am animating the frame of an NSImageView to resize and move the image view. While the frame (size and position) of the NSImageView smoothly moves to the new position, the size of the image view's image is changing instantly when the animation begns, instead of gradually over the animation duration. How can I make the size of the image change smoothly together with the size of the frame?

[NSAnimationContext runAnimationGroup:^(NSAnimationContext * _Nonnull context) {
    // Animate
    [context setDuration:3.0];
    [context setTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut]];
    [[self.imageView animator] setFrame:stage.frame];
} completionHandler:^{
    // Done
}];

The image view has its scaling mode set to NSImageScaleProportionallyUpOrDown.

The new frame may or may not have the same aspect ratio as the old one.

I guess there must be an easy way to do this...?