Twitter Grents (inactive)
Credence 9/10 (Tubin is dead, Grents is a secondary source)
What I understand his elaborations were 'inspired' by a Kivine Paavo book on Keres (including letter correspondence between the close friends Keres/Tubin, reproduced interviews of Tubin's son).
This Estonian acticle 'Tundmatu Keres ehk Miks malesuurusel ei lubatud maailmameistriks saada'
with comments (behind a paywall, but fortunately unlockable when fed into specific translators) by Andres Vaher, 2015 on 'Eesti Päevaleht'-Online was quite informative.
Again it's up to each the (Estonian) reader to judge the writing style of the book if he/she believes the stories. Gents [who has been awarded a Rector's Prize for his outstanding study results and an exceptional bachelor thesis, see below] does not strike me as a character selling an English audience bogus stories for attention. Still somehow he seems to have moved on.
Did this site not have Estonian 'experts' around here before ...
Keres playing chess in Tartu 1944/45
The Complexities of Hybrid Warfare: A study in ContemporaryMilitary History
On a different topic
Browne vs Keres, 1975 (kibitz #22)
expanding a bit on tympsa's great posting
The Real Coodabeen Champion
'.. It has long been speculated in Estonia that Keres was required to throw his games to eventual winner Mikhail Botvinnik in the 1948 World Championship tournament, though no documentary evidence to support this has ever been produced and neither player ever ‘confessed’.
There is no doubt that Keres was never completely trusted by the Soviet authorities, as shown by the cancellation of his Australian tour in the late 1960s.
The day before Keres was to board his plane to Sydney, he was told that permission to travel had been cancelled, apparently for fear of establishing links with Australia’s largely anti-communist Estonian community. (Relations between Australia and the USSR had already foundered earlier in the decade after Australia refused to extradite an Estonian immigrant, Ervin Viks, for war crimes during WWII. A 1987 Australian inquiry, after Viks had died, found that Viks was responsible for the death of at least 18,000 people.) ..'
from 'Gardiner Chess' website by Ian Rogers
War crimes trials in Soviet Estonia [1960s]