When working on an unrelated project, I ended up finding myself looking at another potential Holbein miniature with the Royal Collection Trust.
When enhancing this photograph, there is obviously blackwork embroidery on the man's collar. This portrait does look like it's been inspired by Holbein. As the RCT states, "The art of miniature painting was still in its infancy during the first quarter of the sixteenth century." Perhaps this miniature was painted in Hans Holbein the Younger's workshop? Maybe it was painted by Lucas Horenbout or Susanna Horenbout, or another artist?
According to the RCT, "The locket in which the miniature was originally framed bears an
inscription identifying the sitter as Guildford and the artist as Hans
Holbein the Younger... Examination of the technique used suggests that the miniature may be a
contemporary work of c. 1530–5, although by a less skilful hand than
Holbein’s." Guildford is in reference to "Sir Henry Guildford (1489–1532), Comptroller of the Royal Household to
Henry VIII, was incorrect, but unsurprising. Guildford is shown at the
age of 38 in a portrait by Hans Holbein the Younger dated 1527 in the
Royal Collection (RCIN 400046) and cannot therefore be the much younger
man represented in this near-contemporary miniature, despite the
superficial resemblance between the two figures, and the similar,
assertive pose deployed in both images."
Above is the portrait of Sir Henry Guildford, painted by Hans Holbein the Younger in 1527. The man in the above miniature looks too young, especially for being painted circa 1530-1535, compared to this other portrait of Guildford. So, most likely not the same man and therefore incorrect, as quoted by the RCT above. Guildford was married twice, but did not have any children.
Regardless of who the sitter was, I am fascinated by the blackwork embroidery present!
This is my interpretation of the embroidery pattern found in columns along the collar in the sitter's miniature portrait.