Complex sentence: The portrait seems to date from Holbein's second visit to England, when the sitter was acting on behalf of Henry VIII and commissioned a series of propagandistic images of favoured courtiers at a time when Cromwell's reputation was at its highest.
Split into simpler sentences: The portrait seems to date from Holbein's second visit to England, when the sitter was acting on behalf of Henry VIII and comissioned a series of proparatongastic images of favoured courtiers. It came at a time when Cromwell's reputation was at its highest.