No attorney licensed to practice law in Texas may be disciplined for Professional Misconduct occurring more than four years before the time when the allegation of Professional Misconduct is brought to the attention of the Office of Chief Disciplinary Counsel, except in cases in which disbarment or suspension is compulsory. Limitations will not begin to run where fraud or concealment is involved until such Professional Misconduct is discovered or should have been discovered in the exercise of reasonable diligence by the Complainant.
Tex. R. Disc. P. 17.06