She married and had children with all 3 of her brothers.

http://www.livius.org/la-ld/laodice/laodice_iv.html Laodice IV

Laodice IV: Seleucid queen, wife of Seleucus IV Philopator and Antiochus IV Epiphanes. Relatives:

• Father: Antiochus III the Great
• Mother: Laodice III
• First husband: her brother Antiochus
• Daughter:

1. Nysa (married to Pharnaces of Pontus)

• Second husband: her brother Seleucus IV Philopator

1. Son: Antiochus
2. Son: Demetrius I Soter
3. Daughter: Laodice V

• Third husband: her brother Antiochus IV Epiphanes

1. Son: Antiochus V Eupator
2. Daughter: Laodice VI
3. Son: Alexander I Balas (spurious) Laodice was of Greek Macedonian and Persian descent. She was one of the daughters and among the children born to the Seleucid Monarchs Antiochus III the Great and Laodice III.[1] Her paternal grandparents were the former Seleucid Monarchs Seleucus II Callinicus and Laodice II, while her maternal grandparents were King Mithridates II of Pontus and his wife Laodice. The parents of Laodice IV were first cousins, because her paternal grandfather and with her maternal grandmother were brother and sister, and were among the children of Antiochus II Theos and Laodice I.[2] She was born and raised in the Seleucid Empire. Laodice was commemorated with an honorific inscription dedicated to her at Delos.[3]

Ancestry[edit] [show]Ancestors of Laodice IV First Marriage[edit] In 196 BC, her eldest brother, crown prince Antiochus, was appointed by her father to succeed him.[5] In that year Antiochus III married Laodice to her eldest brother, crown prince Antiochus. The marriage of Laodice IV and Antiochus was the first sibling marriage to occur in the Seleucid dynasty.[6] From their sibling union Laodice IV bore Antiochus a daughter called Nysa.[7] Antiochus III appointed Laodice in 193 BC, as the chief priestess of the state cult dedicated to her late mother Laodice III in Media.[8][9] Later that year, her brother-husband died. The family were in complete grief of his death, in particular Antiochus III.[10]

Second Marriage[edit] Antiochus III arranged for her to marry for a second time her second eldest brother Seleucus IV Philopator.[11] Seleucus IV became co-ruler with their father and was appointed as their father’s successor. In their union, they had three children, two sons: Antiochus, Demetrius I Soter and a daughter called Laodice V.[12] In 187 BC, her father died and her second husband succeeded their father. Seleucus IV became the Seleucid King and Laodice IV became the Seleucid Queen. They reigned as the Seleucid imperial couple from 187 BC until 175 BC, when Seleucus IV died.[13] There is no surviving record on how Laodice IV, reigned as queen or how her contemporaries viewed her. Briefly in 175 BC, Laodice’s first son was briefly King.[14] There are surviving coins dating from 175 BC, that show portraits of Laodice IV and her first son with Seleucus IV, Antiochus making them the first Seleucid King and Queen depicted on coins.[15]

Third Marriage[edit] After the death of Seleucus IV, Laodice married for the third time her youngest brother Antiochus IV Epiphanes. Antiochus IV succeeded his second eldest brother as King. Antiochus IV co-ruled with his nephew Antiochus and adopted him as his son. Antiochus IV had his adopted son assassinated in 170 BC.[16] Laodice bore Antiochus IV two children: a son Antiochus V Eupator and a daughter Laodice VI.[17] When Laodice’s youngest brother and first son co-ruled, her second son Demetrius I Soter was sent as a political hostage in Rome. When Antiochus IV died the first son of Laodice IV and Antiochus IV, Antiochus V Eupator succeeded his father as Seleucid King.[18]

Laodice IV

Laodice IV (flourished second half 3rd century BC and first half 2nd century BC) was a Greek Princess, Head Priestess and Queen of the Seleucid Empire.

Family & Early Life

Laodice was of Greek Macedonian and Persian descent. She was one of the daughters and among the children born to the Seleucid Monarchs Antiochus III the Great and Laodice III. Her paternal grandparents were the former Seleucid Monarchs Seleucus II Callinicus and Laodice II, while her maternal grandparents were King Mithridates II of Pontus and his wife Laodice. The parents of Laodice IV were first cousins, because her paternal grandfather and with her maternal grandmother were brother and sister, and were among the children of Antiochus II Theos and Laodice I. She was born and raised in the Seleucid Empire. Laodice was commemorated with an honorific inscription dedicated to her at Delos.

First Marriage

In 196 BC, her eldest brother, crown prince Antiochus, was appointed by her father to succeed him. In that year Antiochus III married Laodice to her eldest brother, crown prince Antiochus. The marriage of Laodice IV and Antiochus was the first sibling marriage to occur in the Seleucid dynasty.[6] From their sibling union Laodice IV bore Antiochus a daughter called Nysa. Antiochus III appointed Laodice in 193 BC, as the chief priestess of the state cult dedicated to her late mother Laodice III in Media. Later that year, her brother-husband died. The family were in complete grief of his death, in particular Antiochus III.

Second Marriage

Antiochus III arranged for her to marry for a second time her second eldest brother Seleucus IV Philopator. Seleucus IV became co-ruler with their father and was appointed as their father’s successor. In their union, they had three children, two sons: Antiochus, Demetrius I Soter and a daughter called Laodice V. In 187 BC, her father died and her second husband succeeded their father. Seleucus IV became the Seleucid King and Laodice IV became the Seleucid Queen. They reigned as the Seleucid imperial couple from 187 BC until 175 BC, when Seleucus IV died. There is no surviving record on how Laodice IV, reigned as queen or how her contemporaries viewed her. Briefly in 175 BC, Laodice’s first son was briefly King. There are surviving coins dating from 175 BC, that show portraits of Laodice IV and her first son with Seleucus IV, Antiochus making them the first Seleucid King and Queen depicted on coins.

Third Marriage

After the death of Seleucus IV, Laodice married for the third time her youngest brother Antiochus IV Epiphanes. Antiochus IV succeeded his second eldest brother as King. Antiochus IV co-ruled with his nephew Antiochus and adopted him as his son. Antiochus IV had his adopted son assassinated in 170 BC. Laodice bore Antiochus IV two children: a son Antiochus V Eupator and a daughter Laodice VI. When Laodice’s youngest brother and first son co-ruled, her second son Demetrius I Soter was sent as a political hostage in Rome. When Antiochus IV died the first son of Laodice IV and Antiochus IV, Antiochus V Eupator succeeded his father as Seleucid King.

Source :

https://en.wikipedia.org/wiki/Laodice_IV