Glenrothes in owned by Berry Bros? That's news for me.
As far as I know, Glenrothes is owned by Highland Distillers, who also own among other thing Macallan and Highland Park). Highland Distillers is again a non-listed company jointly owned by Edrington and Wm Grant.
Edrington is 100% owned by The Robertson Trust, while Wm Grant still is owned by the Grant-family.
BBR is, as far as I know, still family owned.
A visit to the Edrington webpage gave the following information:
Edrington has supplied Berry Bros with blended whisky for Cutty Sark since 1936, and is today responsible for all aspects of producing Cutty Sark. This through a long-standing partnership. In 1998 they jointly created the company Cutty Sark International, which is responsible for all aspects of marketing and selling Cutty Sark and Glenrothes.