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. Peter has also prepared his own chart on the Relationships of European Sovereigns at the Accession of Elizabeth I of England (1558).