The Doctor perked up a tiny bit at that, at the idea that the regeneration might not have been his fault, that he might not have just deliberately killed a version of the Master, however twisted that version had been.
Jack stood pretty much stunned, gazing anxiously at the Doctor. Eventually, he regained enough co-ordination to rub gently at the Doctor's back, as he said to Romana lips stiff, "The sane Master regenerated too? Was it - it wasn't because he was wasn't recovered from what he did for me, was it?"