I've omitted the principalities, as well as Montenegro and Serbia, due to their rulers' lack of genealogical connections at the time to the others (other than King Nikola I of Montenegro being the father-in-law--not a blood relation--of Peter I of Serbia and Vittorio Emanuele III of Italy). "c"=cousin, "r"=removed, so "4c1r" means "fourth cousin once removed." The table should be read, "(name at left) is the (relationship) of (name on top)," e.g., King Albert I of Belgium was the nephew of King Carol I of Romania. The most recent common ancestor, from whom the relationship is calculated, is given in parentheses; keys to those abbreviations are below.
| Franz Joseph I | Carol I | Alfonso XIII | Ferdinand I | Wilhelm II | Wilhelmina | Nicholas II | Vittorio Emanuele III | Haakon VII | Gustaf V | Albert I | George V | Marie Adelaide | Christian X | Constantine I | |
| Franz Joseph I of Austria-Hungary | -- | 2c (KLB) | 2c1r (L2HRE) | 2c (F1-2S) | 5c1r (LRBW) | 5c (JWF) | 5c1r (LRBW) | 1c2r (M1B) | 1c3r (M1B) | 1c2r (M1B) | 2c1r (KLB) | 5c1r (LRBW) | 3c1r (C3S) | 1c3r (M1B) | 5c1r (LRBW) |
| Carol I of Romania | 2c (KLB) | -- | 5c1r (JWF) | 6c1r (ESGA) | 3c1r (L9HD) | 5c (JWF) | 2c1r (KLB) | 2c2r (KLB) | 4c2r (CdB) | 4c1r (CdB) | uncle (KAH) | 6c (K1HK) | 5c1r (JWF) | 4c2r (CdB) | 5c1r (JWF) |
| Alfonso XIII of Spain | 2c1r (L2HRE) | 5c1r (JWF) | -- | 2c2r (F1-2s) | 5c1r (G2GB) | 4c1r (W4) | 5c1r (G2GB) | 3c (L2HRE) | 5c1r (G2GB) | 2c1r (FWN) | 3c1r (F1-2S) | 5c1r (G2GB) | 3c (FWN) | 5c1r (G2GB) | 3c (LW) |
| Ferdinand I of Bulgaria | 2c (F1-2S) | 6c1r (ESGA) | 2c2r (F1-2S) | -- | 2c1r (FSC) | 4c1r (FA2) | 4c1r (FA2) | 2c2r (F1-2S) | 4c1r (FA2) | 4c2r (FA2) | 1c1r (LP) | 2c1r (FSC) | 3c1r (C3S) | 4c1r (FA2) | 4c1r (FA2) |
| Wilhelm II of Germany | 5c1r (LRBW) | 3c1r (L9HD) | 5c1r (G2GB) | 2c1r (FSC) | -- | 2c1r (P1R) | 2c1r (FW3) | 4c1r (L9HD) | 2c1r (FW3) | 4c (FEW) | 2c1r (FSC) | 1c (QV) | 5c1r (G2GB) | 2c1r (FW3) | 2c1r (FW3) and brother-in-law |
| Wilhelmina of the Netherlands | 5c (JWF) | 5c (JWF) | 4c1r (W4) | 4c1r (FA2) | 2c1r (P1R) | -- | 2c1r (P1R) | 4c2r (JWF) | 2c1r (W1N) | 1c1r (WN) | 5c1r (JWF) | 4c2r (FLW) | 2c (WN) | 2c1r (W1N) | 4c (CCNW) |
| Nicholas II of Russia | 5c1r (LRBW) | 2c1r (KLB) | 5c1r (G2GB) | 4c1r (FA2) | 2c1r (FW3) | 2c1r (P1R) | -- | 3c1r (KLB) | 1c (C9) | 4c (FEW) | 3c (KLB) | 1c (C9) | 2c1r (WHK) | 1c (C9) | 1c (C9) |
| Vittorio Emanuele III of Italy | 1c2r (M1B) | 2c2r (KLB) | 3c (L2HRE) | 2c2r (F1-2S) | 4c1r (L9HD) | 4c2r (JWF) | 3c1r (KLB) | -- | 3c1r (M1B) | 3c (M1B) | 3c1r (KLB) | 6c (LRBW) | 4c (C3S) | 3c1r (M1B) | 6c (LRBW) |
| Haakon VII of Norway | 1c3r (M1B) | 4c2r (CdB) | 5c1r (G2GB) | 4c1r (FA2) | 2c1r (FW3) | 2c1r (W1N) | 1c (C9) | 3c1r (M1B) | -- | 1c1r (O1) | 4c1r (FA2) | 1c (C9) and brother-in-law | 2c1r (WHK) | brother (F8) | 1c (C9) |
| Gustaf V of Sweden | 1c2r (M1B) | 4c1r (CdB) | 2c1r (FWN) | 4c2r (FA2) | 4c (FEW) | 1c1r (WN) | 4c (FEW) | 3c (M1B) | 1c1r (O1) | -- | 4c2r (FA2) | 4c1r (FLW) | 1c1r (WN) | 1c1r (O1) | 3c1r (CCNW) |
| Albert I of Belgium | 2c1r (KLB) | nephew (KAH) | 3c1r (F1-2S) | 1c1r (LP) | 2c1r (FSC) | 5c1r (JWF) | 3c (KLB) | 3c1r (KLB) | 4c1r (FA2) | 4c2r (FA2) | -- | 2c1r (FSC) | 4c (C3S) | 4c1r (FA2) | 4c1r (FA2) |
| George V of the United Kingdom | 5c1r (LRBW) | 6c (K1HK) | 5c1r (G2GB) | 2c1r (FSC) | 1c (QV) | 4c2r (FLW) | 1c (C9) | 6c (LRBW) | 1c (C9) and brother-in-law | 4c1r (FLW) | 2c1r (FSC) | -- | 2c1r (WHK) | 1c (C9) | 1c (C9) |
| Marie Adelaide of Luxembourg | 3c1r (C3S) | 5c1r (JWF) | 3c (FWN) | 3c1r (C3S) | 5c1r (G2GB) | 2c (WN) | 2c1r (WHK) | 4c (C3S) | 2c1r (WHK) | 1c1r (WN) | 4c (C3S) | 2c1r (WHK) | -- | 2c1r (WHK) | 2c1r (WHK) |
| Christian X of Denmark | 1c3r (M1B) | 4c2r (CdB) | 5c1r (G2GB) | 4c1r (FA2) | 2c1r (FW3) | 2c1r (W1N) | 1c (C9) | 3c1r (M1B) | brother (F8) | 1c1r (O1) | 4c1r (FA2) | 1c (C9) | 2c1r (WHK) | -- | 1c (C9) |
| Constantine I of Greece | 5c1r (LRBW) | 5c1r (JWF) | 3c (LW) | 4c1r (FA2) | 2c1r (FW3) and brother-in-law | 4c (CCNW) | 1c (C9) | 6c (LRBW) | 1c (C9) | 3c1r (CCNW) | 4c1r (FA2) | 1c (C9) | 2c1r (WHK) | 1c (C9) | -- |
C3S=King Carlos III of Spain (1716-1788) and Maria Amalia of Saxony
C9=King Christian IX of Denmark (1818-1906) and Louise of Hesse-Kassel (daughter of WHK)
CCNW=Carl Christian, Prince of Nassau-Weilburg (1735-1788) and Caroline of Orange (daughter of W4)
CdB=Claude de Beauharnais (1680-1738), Seigneur de Beaumont, and Renée Hardouineau
ESGA=Ernst I, Duke of Saxe-Gotha and Altenburg (1601-1676) and Elizabeth Sophie of Saxe-Altenburg
F1-2S=King Ferdinando I of the Two Sicilies (1751-1825) (son of C3S) and Maria Carolina of Austria
F8=King Frederik VIII of Denmark (1843-1912) (son of C9) and Louise of Sweden
FA2=Ferdinand Albrecht II, Duke of Brunswick-Lüneburg (1680-1735) and Antonia Amalia of Brunswick (daughter of LRBW)
FSC=Franz, Duke of Saxe-Coburg-Saalfeld (1750-1806) and Augusta of Reuss-Ebersdorff
FEW=Friedrich Eugen, Duke of Württemberg (1732-1797) and Dorothea of Brandenburg-Schwedt
FLW=Frederick Lewis, Prince of Wales (1707-1751) (son of G2GB) and Augusta of Saxe-Gotha
FW3=King Friedrich Wilhelm III of Prussia (1770-1840) and Luise of Mecklenburg-Strelitz
FWN=Friedrich Wilhelm of Nassau (1768-1816) (son of CCNW) and Louise von Kirchberg
G2GB=King George II of Great Britain (1683-1760) and Caroline of Ansbach
JWF=Jan Willem Friso, Prince of Orange (1686-1711) and Marie Louisa of Hesse-Kassel (daughter of K1HK)
K1HK=Karl I, Landgrave of Hesse-Kassel (1654-1730) and Maria Amalia of Courland
KAH=Karl Anton, Prince of Hohenzollern (1811-1885) and Josephine of Baden
KLB=Karl Ludwig of Baden (1755-1801) and Amalia of Hesse (daughter of L9HD)
L2HRE=Holy Roman Emperor Leopold II (1747-1792) and Maria Luisa of Spain (daughter of C3S)
L9HD=Ludwig IX, Landgrave of Hesse-Darmstadt (1719-1790) and Caroline of Zweibrücken
LP=King Louis Philippe of the French (1773-1850) and Marie Amelie of the Two Sicilies (daughter of F1-2S)
LRBW=Ludwig Rudolf, Duke of Brunswick-Blankenburg & Wölfenbüttel (1671-1735) and Christine Louise of Öttingen
LW=Ludwig of Wurttemberg (1756-1817) (son of FEW) and Henrietta of Nassau (daughter of CCNW)
M1B=King Maximilian I of Bavaria (1756-1825) and Augusta of Hesse (Scandinavian descendants) or Caroline of Baden (daughter of KLB) (Austrian and Italian descendants)
O1=King Oscar I of Sweden (1799-1859) and Josephine of Leuchtenberg (granddaughter of M1B)
P1R=Emperor Paul I of Russia (1754-1801) and Sophia of Württemberg (daughter of FEW)
QV=Queen Victoria of Great Britain (1819-1901) and Albert of Saxe-Coburg
W1N=King Willem I of the Netherlands (1772-1842) and Wilhelmina of Prussia (sister of FW3)
W4=Willem IV, Prince of Orange (1711-1751) (son of JWF) and Anne of Great Britain (daughter of G2GB)
WHK=Wilhelm of Hesse-Kassel (1787-1867) and Charlotte of Denmark
WN=Wilhelm, Duke of Nassau (1792-1839) (son of FWN) and Louise of Saxe-Altenburg (Luxembourg descendants) or Pauline of Württemberg (Scandinavian and Dutch descendants)
Relationships of Current European Sovereigns
I am grateful to forum member Peter for his help in revising and refining these tables.