Who plays Greer in Reign?

Greer is played by Celina Sinden.

How is Greer connected to other characters?

Greer has 3 mapped relationships in Reign. Explore the interactive relationship map for details.

Greer — Royal household colleagues — Mary Stuart (Adelaide Kane)
Their professional roles overlap within the royal household, where personal loyalty supports official service.

Greer serves in Mary's household from the pilot onward and remains involved in court missions and protective schemes.
Greer — Extended family by marriage — Stéphane Narcisse (Craig Parker)
The available plot establishes court-family links around Narcisse's household, but does not provide enough evidence for a direct intimate bond between Greer and Narcisse.

Greer marries Aloysius Castleroy in the broader court conflict, and S4E4 states that Claude is arranged to marry Narcisse's son Luc.
Greer — Factional opponents — John Knox (Jonathan Goad)
Their opposition is primarily factional; the supplied episodes do not establish a sustained personal confrontation.

Knox leads opposition to the Scottish monarchy in S3E17 and later works with anti-Mary nobles in S4E12-S4E16, while Greer remains aligned with Mary.