11 January] 1890 – 28 August 1979) was the third child and eldest daughter of Grand Duke Constantine Constantinovich of Russia and his wife, Princess Elisabeth of Saxe-Altenburg.

She was close friends with Tsar Nicholas II's two eldest daughters, Olga and Tatiana Nikolaevna, and was mentioned frequently in both their diaries.

Earlier that morning, she left the Palace of Strelna, which was nearby, in a string of carriages, which went along the Finnish Gulf before reaching the Emperor's estate.

She was said to be wearing "long white gloves"[citation needed] with "a string of her mother's pearls around her neck, and a satin kokoshnik with a large bow atop her hair.

In the spring of 1911, Tatiana Constantinovna became engaged to Prince Constantine Bagration of Mukhrani (14 March 1889, Tbilisi, - 1 June 1915, Jarosław), a Georgian by birth who was serving in a Russian Imperial Guards regiment, and died in World War I.

The grand dukes officially petitioned the Emperor through a commission chaired by Grand Duke Nicholas Nikolayevich of Russia, requesting that a new category of dynastic marriages be recognized, to consist of Imperial princes and princesses entitled, with specific Imperial consent, to marry persons of non-royal blood and to transmit to the issue thereof eligibility to inherit the throne.

Also remaining unrepealed was article 36 ("Children born of a marriage between a member of the Imperial Family and a person not of corresponding rank, that is, not belonging to a Royal or Ruling House, shall have no right of succession to the Throne").

The Emperor was present at the wedding and, according to a family tradition subsequently repeated by the bride's son, Nicholas II is reported to have suggested that the bridegroom sign the wedding register as "Prince Gruzinsky", perhaps a courteous acknowledgement of the fact that, although for the preceding century the Bagrations might only rank as nobles who bore the fairly common title of Knyaz (prince) in Russia, historically the Mukhranskys were a branch of a deposed royal dynasty that had ruled on both sides of the Caucasus for hundreds of years longer than the Romanovs.

"[5] Tatiana and Prince Constantine Bagration of Mukhrani had two children: After the outbreak of World War I, Konstantin enlisted in Russia's armed forces, and was killed in action in 1915.

Tatiana raised her children alone, giving them the best education she possibly could, and, after both were grown and married, she took the veil, in Switzerland in 1946, just after the end of the second World War, which was her father's dream.

She later served as Abbess at the Mount of Olives Convent in Jerusalem, and died as Mother Tamara (named so after the medieval Georgian queen Tamar, a remote ancestor of Tatiana's first husband),[7] on 28 August 1979.

In post-monarchy debates over which pretender has the strongest claim to Russia's throne under the dynastic laws, the marriage of Tatiana Konstantinovna is often cited in support of rival claimants.

An oft-heard rebuttal is that the Bagrations fall into the same "grey area" as the 1856 marriage of Grand Duchess Maria Nikolayevna to Duke Maximilian of Leuchtenberg, who was not a member of a "royal or ruling family", despite his historical dynastic connections, yet Emperor Nicholas I exercised Imperial authority to rule in favor of Duke Maximilien's dynasticity for marital purposes.

First, they maintain that Nicholas II's acceptance of Tatiana Konstantinovna's renunciation prior to marriage explicitly confirms that she had succession rights despite being born of a Lutheran mother who never converted to the Russian Orthodox Church, which is a prerequisite for successors to Russia's throne.

A rebuttal is that article 185 of the Pauline laws is explicit: "The marriage of a male member of the Imperial House who might succeed to the Throne to a person of another faith may not take place until she embraces Orthodoxy."

The second relevant claim in support of Maria Vladimirovna is that Tatiana Konstantinovna's mandated renunciation proves that Romanov princes were required to marry "equally" in order to transmit succession rights to their descendants, an interpretation denied by Nicholas Romanovich Romanoff, former president of the Romanoff Family Association, in an interview with the royalty magazine, Point de Vue, published 14 February 1991, who stated, "Let’s take the example of the Princess Tatiana who, in 1911, married a prince of a very great family of Georgia, but which was not reigning.

The counter-claim has been that the wording of the August 1911 ukase restricting the ban on morganatic marriages to grand dukes was silent on imperial princes, therefore the Frederiks memorandum was not given full legal effect.